Merge branch 'ta/config-set-2'

Update git_config() users with callback functions for a very narrow scope with calls to config-set API that lets us query a single variable. * ta/config-set-2: builtin/apply.c: replace `git_config()` with `git_config_get_string_const()` merge-recursive.c: replace `git_config()` with `git_config_get_int()` ll-merge.c: refactor `read_merge_config()` to use `git_config_string()` fast-import.c: replace `git_config()` with `git_config_get_*()` family branch.c: replace `git_config()` with `git_config_get_string() alias.c: replace `git_config()` with `git_config_get_string()` imap-send.c: replace `git_config()` with `git_config_get_*()` family pager.c: replace `git_config()` with `git_config_get_value()` builtin/gc.c: replace `git_config()` with `git_config_get_*()` family rerere.c: replace `git_config()` with `git_config_get_*()` family fetchpack.c: replace `git_config()` with `git_config_get_*()` family archive.c: replace `git_config()` with `git_config_get_bool()` family read-cache.c: replace `git_config()` with `git_config_get_*()` family http-backend.c: replace `git_config()` with `git_config_get_bool()` family daemon.c: replace `git_config()` with `git_config_get_bool()` family