This lifts a limitation where non-fast-forward updates could only be
allowed for references whose name start with 'refs/heads/' (the
standard namespace for branches). As it happens, GCC is using branch
names in a different namespace. So this commit changes this config
option to match the entire reference name, rather than just the branch
name. There is a break in compatibility for the repositories already
using this configuration, but this change takes care of detecting
this situation and provide an informative message explaining the likely
situation.
Change-Id: I330d15ccef448e815c94a620f008275f1e1914db
TN: T209-002
The fact that utils.py imports config.py makes it difficult for
config.py to access the InvalidUpdate exception. So move this
exception to its own package, free of dependencies.
Preparation work for LC27-007.
