[BUG] string_equal_bits() could return garbage on identical strings
[BUG] string_equal_bits() could return garbage on identical strings

When inserting duplicates on x86/x86_64, the assembler optimization
does not support equal strings that both end up with a zero, and
can return garbage in the bit number, possibly causing a segfault
for its users. The only case where this can happen appears to be
in ebst_insert().

sociomantic-tsunami/ebtree,haproxy/ebtree,sociomantic-tsunami/ebtree