GetPrerequisites: Add support for @rpath on Mac OS X.

Handle @rpath much like other Unixes, by doing a find_file with the given directories.

Also, consider a library to be local if it is found in the same directory or a subdirectory relative to the user
executable/library.  Previously, it was local only if found in the same directory.
This case is encountered when @rpath is used with framework libraries, which are inside a directory tree.

Modules/GetPrerequisites.cmake

@@ -303,6 +303,26 @@ function(gp_resolve_item context item exepath dirs resolved_item_var)
     endif(item MATCHES "@loader_path")
   endif(NOT resolved)
 
+  if(NOT resolved)
+    if(item MATCHES "@rpath")
+      #
+      # @rpath references are relative to the paths built into the binaries with -rpath
+      # We handle this case like we do for other Unixes
+      #
+      string(REPLACE "@rpath/" "" norpath_item "${item}")
+
+      set(ri "ri-NOTFOUND")
+      find_file(ri "${norpath_item}" ${exepath} ${dirs} NO_DEFAULT_PATH)
+      if(ri)
+        #message(STATUS "info: 'find_file' in exepath/dirs (${ri})")
+        set(resolved 1)
+        set(resolved_item "${ri}")
+        set(ri "ri-NOTFOUND")
+      endif(ri)
+
+    endif(item MATCHES "@rpath")
+  endif(NOT resolved)
+
   if(NOT resolved)
     set(ri "ri-NOTFOUND")
     find_file(ri "${item}" ${exepath} ${dirs} NO_DEFAULT_PATH)
@@ -458,12 +478,16 @@ function(gp_resolved_file_type original_file file exepath dirs type_var)
 
     if(NOT is_system)
       get_filename_component(original_path "${original_lower}" PATH)
-      get_filename_component(path "${lower}" PATH)
-      if("${original_path}" STREQUAL "${path}")
+      string(LENGTH "${original_path}/" original_length)
+      string(LENGTH "${lower}" path_length)
+      if(${path_length} GREATER ${original_length})
+        string(SUBSTRING "${lower}" 0 ${original_length} path)
+        if("${original_path}/" STREQUAL "${path}")
           set(is_local 1)
         endif()
       endif()
     endif()
+  endif()
 
   # Return type string based on computed booleans:
   #