Trac# 19900
Issue=291

- add an 'uncompile' function to clear all results from any previous compile attempts
- allow compiling to be done multiple times on the same shader
- allow a shader to be compiled with no source specified (to produce an appropriate error).

Signed-off-by: Shannon Woods
Signed-off-by: Nicolas Capens

git-svn-id: https://angleproject.googlecode.com/svn/trunk@991 736b8ea6-26fd-11df-bfd4-992fa37f6226