color: restore _style global after debugcolor ran Before this change, running 'debugcolor' would destroy all color style for the rest of the process life. We now properly backup and restore the variable content. Using a global variable is sketchy in general and could probably be removed. However, this is a quest for another adventure.

color: add basic documentation to 'debugcolor' This does not hurt.

tests: merge 'test-push-hook-lock.t' into 'test-push.t' That test file is very small and is merge with the new 'test-push.t'. No logic is changed. We don't register this as a copy because is actually a "ypoc" merging two file together without replacing the destination and Mercurial cannot express that.