Rename IslTextureTarget to IsInternalTextureTarget.

TEXTURE_EXTERNAL is not considered an internal texture target.
Review URL: https://codereview.appspot.com/5556067

git-svn-id: https://angleproject.googlecode.com/svn/trunk@955 736b8ea6-26fd-11df-bfd4-992fa37f6226
diff --git a/src/libGLESv2/utilities.cpp b/src/libGLESv2/utilities.cpp
index 6dc419c..6589eb1 100644
--- a/src/libGLESv2/utilities.cpp
+++ b/src/libGLESv2/utilities.cpp
@@ -328,7 +328,7 @@
     return (target >= GL_TEXTURE_CUBE_MAP_POSITIVE_X && target <= GL_TEXTURE_CUBE_MAP_NEGATIVE_Z);
 }
 
-bool IsTextureTarget(GLenum target)
+bool IsInternalTextureTarget(GLenum target)
 {
     return target == GL_TEXTURE_2D || IsCubemapTextureTarget(target);
 }