Bug 1105128 - Avoid excessive path normalization in FileCopier.copy(); r=glandium

FileCopier.copy() was performing a lot of os.path.normpath() operations.
Profiling revealed that os.path.normpath() was the function with the
most wall time CPU usage when processing the tests manifests. Upon
subsequent examination of the code in question, all the paths being used
were already normalized. So, os.path.normpath() wasn't accomplishing
anything.

This patch results in ~300ms reduction in wall time to process the tests
install manifest on a fully populated page cache. Execution time drops
from ~2.8s to ~2.5s.

Profiling reveals that after this patch os.stat() is the #1 wall time
consumer. However, os.path.{join,dirname,normpath} still account for
~1.5x the wall time of os.stat(). There is still room to optimize
this function.

--HG--
extra : rebase_source : b6f0862baa5168c609499fd95eb3517854bc8cce
extra : amend_source : 7e04c1eb74132bbbe86e721f0f209b19309a7a51
Bug 1105128 - Alias os.path functions in local scope; r=glandium

Various os.path attributes are being used in tight loops. Having local
variables prevents extra dictionary lookups.

This appears to shave 10-20ms off of the tests install manifest
processing time.

--HG--
extra : rebase_source : de941f2978cf0b1fd7c4f7401c848b61d406a2c8
extra : amend_source : e33c896856fa559197496b8227e10ab8149d146e