Enhance the support for specifying directories and files to gtags

[Suresh Govindachar]

Hello,

  At present, the -f option to gtags only allows file names.  
  Please consider supporting gtags to be called with a list 
  of project directories, perhaps:

    gtags -p /path/first/project,/path/second/project [dbpath]

  Also, consider supporting wild-card based options for to \
  exclude files and directories.

  More generally:

  The directory specification for rsync 
http://rsync.samba.org/ftp/rsync/rsync.html
  gives the user lots of control over the various directories and 
  files involved in the rsync command.  It would help if gtags
  gave the user more control over the project directories and files.

  Thanks,

  --Suresh