Quick GTMStackTrace fix.

I noticed that the format specifier in GTMStackTrace was expecting to print out a hex address preceded by 0X, but the address won't actually be preceded by OX. Adding a # to the format specifier should fix this, I think.

I'm not quite sure how to test this change...?

DELTA=2  (0 added, 0 deleted, 2 changed)

git-svn-id: http://google-toolbox-for-mac.googlecode.com/svn/trunk@631 7dc7ac4e-7543-0410-b95c-c1676fc8e2a3