Check short needle string routines

There's been discussion on the libc-alpha list about short needle specialised routines of strstr, strcasestr and memmem:
 http://sourceware.org/ml/libc-alpha/2012-06/msg00027.html

Michael thinks there might be others. We know from Dave's work that the str* routines are typically called with very short strings.

Check:
 * If the above routines need changes for ARM
 * If the short needle approach helps for strcmp, strlen, etc
 * The benchmarks used (libosip, +1) to see if they help our work