sync file with diff.git 279d77aa1e4b921090e702a6a8a5a94a98a062b1 and use the faster headers-only mode for diff3

got: don't search through ignored paths and files on commit

gotwebd: kill unused id_str in got_output_repo_tree ok stsp@

gotwebd: avoid extra strdups in got_output_repo_tree ok stsp@

gotwebd: avoid extra variable in got_output_repo_tree in_repo_path was used only to build a path, it's then assigned to path (which is NULL at that point.) Just asprintf into path. ok stsp@

Do not segfault verifying "lightweight" tags ok stsp@

gotwebd: plugs leaks in got_get_repo_commits call got_get_repo_commit only once and avoid leaking the field of repo_commit at each loop iteration. ok stsp@

gotwebd: free in_repo_path in got_get_repo_commits; ok stsp@

gotwebd: always free ref in got_get_repo_commits some code-paths may leak it. ok stsp@

gotwebd: don't close tag in got_get_repo_tags too early it's still used a bit later, so defer the free'ing at the next loop iteration or at function end.

gotwebd: free commit_msg0 only at the end of got_get_repo_tags in case of a failure between when it's allocated and when it's released it might get leaked otherwise. ok and semplification stsp@

gotwebd: plug some leaks in got_get_repo_tags ok stsp@

gotwebd: free age and reflist in gotweb_render_branches ok stsp@

switch diff output mode from "edscript" to "plain" for diff3 getchange() in diff3.c takes any line that starts with an integer and treats it as a hunk header. It doesn't actually require ed script instructions, and traditional ed script diff output would break it. Thus, changing Got's diff3 to rely on plain diff output mode paves the way for implementing traditional ed-script style output in diff.git. Patch by Tom Jones

sync files from diff.git 810479a563ffd6176105f64cb49f9829d45d36df