Add/fix some license notices. * lib/mcel.c: Use same license notice as lib/mcel.h. * lib/same-inode.c: Use same license notice as lib/same-inode.h. * lib/str_startswith.c: Change license notice to LGPLv2+. * lib/str_endswith.c: Likewise. * lib/hash-triple.h: Change license notice to GPL. * lib/xstring-buffer.c: Likewise. * lib/xstring-buffer-printf.c: Likewise. * lib/xstring-buffer-reversed.c: Likewise. * lib/xstring-buffer-reversed-printf.c: Likewise.