[PATCH 0 of 2] reading and parsing .hg/requires

[Adrian Buehlmann]

Patch 1 is a refactoring that introduces a new function scmutil.readrequires.
The advantage of doing that is having the error handling in a single place
(instead of twice in localrepo.py and statichttprepo.py).

Patch 2 improves the error message that is shown on unknown requires file
entries. There is an example in the change message for patch 2. Please have
a look there. Patch 2 depends on patch 1 by changing the error message in
the new scmutil.readrequires functions (which is introduced by Patch1).