FIND_WITH_DEF()

     Searches for files with a default path and extension.

     Finds files using default paths and extensions, similar to using the
     DEFAULT keyword with the OPEN statement in VMS.  Using this routine
     together with environment variables allows an OS-independent approach
     to finding files.

     Result = FIND_WITH_DEF( FILENAME, PATHS  [, EXTENSIONS ] )

     FILENAME   = Name of file to be searched for.  It may either be a
                    complete filename, or the path or extension could be left
                    off, in which case the routine will attempt to find the
                    file using the default paths and extensions.
     PATHS      = One or more default paths to use in the search in case
                    FILENAME does not contain a path itself.  The individual
                    paths are separated by commas, although in UNIX, colons
                    can also be used.  In other words, PATHS has the same
                    format as !PATH, except that commas can be used as a
                    separator regardless of operating system.  The current
                    directory is always searched first, unless the keyword
                    NOCURRENT is set.
                    A leading $ can be used in any path to signal that what
                    follows is an environmental variable, but the $ is not
                    necessary.  (In VMS the $ can either be part of the path,
                    or can signal logical names for compatibility with Unix.)
                    Environmental variables can themselves contain multiple
                    paths.

     EXTENSIONS = One or more extensions to append to end of filename if the
                    filename does not contain one (e.g. ".dat").  The period
                    is optional.  Multiple extensions can be separated by
                    commas or colons.

     The result of the function is the name of the file if successful, or
     the null string if unsuccessful.

     NOCURRENT = If set, then the current directory is not searched.
      RESET      = The FIND_WITH_DEF routine supports paths which are
                    preceeded with the plus sign to signal that all
                    subdirectories should also be searched.  Often this is
                    used with logical names.  It can be rather slow to search
                    through these subdirectories.  The /RESET keyword can be
                    used to redefine an environment variable so that
                    subsequent calls don't need to look for the
                    subdirectories.
                    To use /RESET, the PATHS parameter must contain the name
                    of a *single* environment variable.  For example
                     setenv,'FITS_DATA=+/datadisk/fits'
                     file = find_with_def('test.fits','FITS_DATA',/reset)

       FILENAME = ''
       READ, 'File to open: ', FILENAME
       FILE = FIND_WITH_DEF( FILENAME, 'SERTS_DATA', '.fix' )
       IF FILE NE '' THEN ...

       BREAK_PATH(), FIND_ALL_DIR(), STR_SEP()

       Version 1, William Thompson, GSFC, 3 May 1993.
               Removed trailing / and : characters.
               Fixed bugs
               Allow for commas within values of logical names.
               Added keyword NOCURRENT.
               Changed to call BREAK_PATH
       Version 2, William Thompson, GSFC, 3 November 1994
               Made EXTENSIONS optional.
       Version 3, William Thompson, GSFC, 30 April 1996
               Call FIND_ALL_DIR to resolve any plus signs.
       Version 4, S.V. Haugan, UiO, 5 June 1996
               Using OPENR,..,ERROR=ERROR to avoid an IDL 3.6
               internal nesting error.
       Version 5, R.A. Schwartz, GSFC, 11 July 1996
               Use SPEC_DIR to interpret PATH under VMS
       Version 6, William Thompson, GSFC, 5 August 1996
               Took out call to SPEC_DIR (i.e., reverted to version 4).  The
               use of SPEC_DIR was required to support logical names defined
               via SETLOG,/CONFINE.  However, it conflicted with the ability
               to use logical names with multiple values.  Removing the
               /CONFINE made it unnecessary to call SPEC_DIR in this routine.
       Version 7, William Thompson, GSFC, 6 August 1996
               Added keyword RESET
       Converted to IDL V5.0   W. Landsman   October 1997
       Use STRTRIM instead of TRIM,   W. Landsman   November 1998
       Use STRSPLIT instead of STR_SEP  W. Landsman  July 2002

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