Drop leading whitespace from file regex.
Drop leading whitespace from file regex.

Tests prefix filenames with a tab, which sublime misinterprets
as part of the filename. We should ignore that.

Change-Id: Ied730dcdb2e9b33aeb544821be209cad8952e0aa
Reviewed-on: https://go-review.googlesource.com/19360
Reviewed-by: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

golang/sublime-build,golang/sublime-build