This patch adds the following three functions:
 bits_to_bytes(bits) - the number of bytes needed to hold 'bits'
 bytes_to_int32(bytes) - the number of 4-byte units to hold 'bytes'
 pad_to_int32(bytes) - the closest multiple of 4 equal to or larger than
                        'bytes'.

All three operations are common in protocol processing and currently the
server has ((foo + 7)/8 + 3)/4 operations all over the place. A common set
of functions reduce the error rate of these (albeit simple) calculations and
improve readability of the code.

The functions do not check for overflow.

v2: backport to nx-libs 3.6.x as a prereq for
the CVE-2015-0255 fix (Mike DePaulo)
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>