gyp_skia: Fix module search path.

gyp_skia should prepend the local gyp source path to the python
module search path, instead of appending it. Otherwise, if a 'gyp'
module is locally installed on the machine, it will be read instead
of the current version in the Skia tree.

This breaks the Android build when the installed 'gyp' module doesn't
support the "make-android" generator.
Review URL: https://codereview.appspot.com/6344096

git-svn-id: http://skia.googlecode.com/svn/trunk@4832 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gyp_skia b/gyp_skia
index cf55084..d6b5504 100755
--- a/gyp_skia
+++ b/gyp_skia
@@ -26,7 +26,9 @@
 # to be written.
 output_dir = os.path.join(os.path.abspath(script_dir), 'out')
 
-sys.path.append(os.path.join(gyp_source_dir, 'pylib'))
+# Ensure we import our current gyp source's module, not any version
+# pre-installed in your PYTHONPATH.
+sys.path.insert(0, os.path.join(gyp_source_dir, 'pylib'))
 import gyp
 
 def additional_include_files(args=[]):