Report stat error when checking if file modified
Set error when no merge base is found
Report errors finding notes
Report a couple object error conditions
Catch some odd odb backend corner case errors

There are some cases, particularly where no loaded ODB backends
support a particular operation, where we would return an error
code without having set an error.  This catches those cases and
reports that no ODB backends support the operation in question.
Report some errors returnable by push
Error messages for a couple other boundary conditions
Factor out some code that needed to clear errors

A number of places were looking up option config values and then
not clearing the error codes if the values were not found.  This
moves the repeated pattern into a shared routine and adds the
extra call to giterr_clear() when needed.
minor missing error message
Fix one error not reported in revparse

There are many paths through revparse that may return an error
code without reporting an error, I believe.  This fixes one of
them.  Because of the backtracking in revparse, it is pretty
complicated to fix the others.
Clear error msg when we eat error silently
clarify where error message is set
clarify error propogation
Add extra locking around packfile open

We were still seeing a few issues in threaded access to packs.
This adds extra locks around the opening of the mwindow to
avoid a different race.
Extra threading tests

We need to hammer the packfile open phase harder in the thread
tests, in addition to the cache API.
Fix some compile warnings and trailing whitespace
Protect sha1_entry_pos call with mutex

There is an occasional assertion failure in sha1_entry_pos from
pack_entry_find_index when running threaded.  Holding the mutex
around the code that grabs the index_map data and processes it
makes this assertion failure go away.
Merge pull request #1529 from arrbee/more-packfile-locking

More packfile locking
refdb_fs: do not require peeled packed refs to be tags

Older versions of git would only write peeled entries for
items under refs/tags/. Newer versions will write them for
all refs, and we should be prepared to handle that.
Revert "Protect sha1_entry_pos call with mutex"

This reverts commit 8c535f3f6879c6796d8107d7eb80dd8b2105621b.