The function is used to query information about a given GPT package metadata file.

     Function name: QueryPkgDataFile
     Inputs:
          pkgdatafile => Location of package data file
          key         => value to query
          type        => used for 'key' equals 'Deps' to specify what type
                         of dependency

     Valid values for 'key' are:
          Name        - Returns a scalar with the name of the package
          Type        - Returns a scalar with the type of the package
          Description - Returns a scalar with the description of the package
          Deps        - Returns an array of name-flavor_type package tuples
                        which are the dependents of the given package.
          Setup_Name  - Returns a scalar with the setup name of the package
                        if one exists, undef otherwise
          Version     - Returns a scalar with the version of the package
          Flavor      - Returns a scalar with the flavor of the package

     * If the 'type' arguement is not set when 'key' equals 'Deps', all 
       dependent packages are returned. Otherwise, only packages of dependency
       type 'type' are returned. Valid values for 'type' are:

          pgm_link, lib_link, data_runtime, doc_runtime, compile,
          pgm_runtime, lib_runtime, rtl_runtime, Setup

       Note that dependency listings are not recursive, the array of tuples
       only includes those dependent package explicitly listed in the package's
       metadata file. In order to recurse that list, the developer should make
       repeated calls to this function with the package data files of
       dependent packages.

Examples:

     my $pkgname = GPTAPI::QueryPkgDataFile(pkgdatafile => "pkg_data_src.gpt.in", 
                                            key         => "Name");
     my $deppkgs = GPTAPI::QueryPkgDataFile(pkgdatafile => "pkg_data_src.gpt.in", 
                                            key         => "Deps",
                                            type        => "compile");