vector: Timsort all of the things

Drop the GLibc implementation of Merge Sort and replace it with Timsort.

The algorithm has been tuned to work on arrays of pointers (void **),
so there's no longer a need to abstract the byte-width of each element
in the array.

All the comparison callbacks now take pointers-to-elements, not
pointers-to-pointers, so there's now one less level of dereferencing.

E.g.

	 int index_cmp(const void *a, const void *b)
	 {
	-	const git_index_entry *entry_a = *(const git_index_entry **)(a);
	+	const git_index_entry *entry_a = (const git_index_entry *)(a);

The result is up to a 40% speed-up when sorting vectors. Memory usage
remains lineal.

A new `bsearch` implementation has been added, whose callback also
supplies pointer-to-elements, to uniform the Vector API again.

1 files changed, 1 insertions, 4 deletions

diff --git a/tests/t00-core.c b/tests/t00-core.c
index 7bcc77aeb..660f10c89 100644
--- a/tests/t00-core.c
+++ b/tests/t00-core.c
@@ -75,10 +75,7 @@ END_TEST
 
 static int test_cmp(const void *a, const void *b)
 {
-	int n1 = *(int *)a;
-	int n2 = *(int *)b;
-
-	return n1 - n2;
+	return a - b;
 }
 
 BEGIN_TEST(vector2, "remove duplicates")