turn on pathops unit test

turn on pathops unit test

This temporarily disables SK_ENABLE_INST_COUNT 
( skbug.com/1219 )

This fixes a linktime error on VS2012 in
PathTest.cpp; -SK_ScalarInfinity should be
SK_ScalarNegativeInfinity instead.

This adds pathops and pathops unit tests to the
main unit tests.

Should this change destabilize anything, it should
be sufficient to comment out the pathops gypi
includes. at test.gyp:18,21.
Committed: https://code.google.com/p/skia/source/detail?r=8644

[caryclark, 2013-04-12 11:59:58]

Committed patchset #2 manually as r8644 (presubmit successful).