Implement global/system file search paths

The goal of this work is to expose the search logic for "global",
"system", and "xdg" files through the git_libgit2_opts() interface.

Behind the scenes, I changed the logic for finding files to have a
notion of a git_strarray that represents a search path and to store
a separate search path for each of the three tiers of config file.
For each tier, I implemented a function to initialize it to default
values (generally based on environment variables), and then general
interfaces to get it, set it, reset it, and prepend new directories
to it.

Next, I exposed these interfaces through the git_libgit2_opts
interface, reusing the GIT_CONFIG_LEVEL_SYSTEM, etc., constants
for the user to control which search path they were modifying.
There are alternative designs for the opts interface / argument
ordering, so I'm putting this phase out for discussion.

Additionally, I ended up doing a little bit of clean up regarding
attr.h and attr_file.h, adding a new attrcache.h so the other two
files wouldn't have to be included in so many places.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/repository.h b/src/repository.h
index ebd797cc1..cc2f8c2b8 100644
--- a/src/repository.h
+++ b/src/repository.h
@@ -19,7 +19,7 @@
 #include "buffer.h"
 #include "odb.h"
 #include "object.h"
-#include "attr.h"
+#include "attrcache.h"
 #include "strmap.h"
 #include "refdb.h"