coyote: CGSOURCEDIR

Description
The purpose of this function is to provide a portable way of finding
the source directory of a program distribution. The directory that is returned
is the directory in which the source file using cgSourceDir() resides.
The program is useful for distributing applications that have a large number
of files in specific program directories (e.g., source, resources, data, etc.).
Categories
Utilities
Keywords
nomark: in, optional, type=boolean, default=0
  Normally, the source directory name is returned with a final path
  separator added to the end of the directory name. Setting this keyword
  will suppress this final path separator.
oneup: in, optional, type=boolean, default=0
   Setting this keyword will return the directory just above the source 
   directory in the file hierarchy.
twoup: in, optional, type=boolean, default=0
    Setting this keyword will return the directory two directories above the source
    directory in the file hierarchy. 
Examples
Assume that your application files (and source programs) reside in this root directory::
      ../app
You have placed a DATA directory immediately under the APP directiory, and a RESOURCES
directory immedately under the DATA directory. Your directory structure looks like this::
      ../app                    ; Contains your application and source (*.pro) files.
      ../app/data               ; Contains your application data files.
      ...app/data/resources     ; Contains your application resource files.
The end user can install the APP directory wherever he or she likes. In your
program, you will identify the DATA and RESOURCES directory like this::
       ; Get icon image in resources directory.
       filename = Filepath(Root_Dir=cgSourceDir(), Subdirectory=['data','resources'], 'myicon.tif')
       ; Get default image in data directory.
       filename = Filepath(Root_Dir=cgSourceDir(), Subdirectory='data', 'ctscan.tif')
Alternatively, you might set up an application directory structure like this::
      ../app                    ; Contains your application files.
      ../app/source             ; Contains your application source (*.pro) files.
      ../app/data               ; Contains your application data files.
      ...app/data/resources     ; Contains your application resource files.
In this case, you would use the ONEUP keyword to find your data and resource files, like this::
       ; Get icon image in resources directory.
       filename = Filepath(Root_Dir=cgSourceDir(/ONEUP), Subdirectory=['data','resources'], 'myicon.tif')
       ; Get default image in data directory.
       filename = Filepath(Root_Dir=cgSourceDir(/ONEUP), Subdirectory='data', 'ctscan.tif')
Author
FANNING SOFTWARE CONSULTING::
   David W. Fanning 
   1645 Sheely Drive
   Fort Collins, CO 80526 USA
   Phone: 970-221-0438
   E-mail: david@idlcoyote.com
   Coyote's Guide to IDL Programming: http://www.idlcoyote.com
History
Change History::
  Written by: David W. Fanning, 23 November 2003. Based on program SOURCEROOT, written by
    Jim Pendleton at RSI (http://www.rsinc.com/codebank/search.asp?FID=35).
  Added ONEUP keyword. 10 December 2003. DWF.
  Added TWOUP keyword. 8 June 2007. DWF.
  Added NOMARK keyword. 8 June 2007. DWF.
  Renamed from ProgramRootDir and updated to cgSourceDir. 27 Jan 2014. DWF.
Copyright
Copyright (c) 2003-2014, Fanning Software Consulting, Inc.