Merge r14229 from the BUF_REMOVAL branch to trunk.
Function MC_(snprintf_delta) requires a buffer of size 31 or larger to
avoid overflow.Add an assert, change and document the buffer size and
fix all call sites. Remove magic constants along the way.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14583 a5019735-40e9-0310-863c-91ae7b9d1cf9