Fix 2 bugs in online::push tests.

- Fix stack corruption introduced in 9bccf33c due to passing pointer to
local variable _cred_acquire_called.
- Fix strcmp in do_verify_push_status when expected or actual push_status
  is NULL
Added git_treebuilder_entrycount

Conflicts:
	src/tree.c
Merge pull request #1289 from jwiegley/development

Added git_treebuilder_entrycount