Fix some printf format warnings

Fix some printf format warnings

commit 51ea551 ("make sure byte swapping is optimal for git"
2009-08-18) introduced a "sane definition for ntohl()/htonl()"
for use on some GNU C platforms. Unfortunately, for some of
these platforms, this results in the introduction of a problem
which is essentially the reverse of a problem that commit 6e1c234
("Fix some warnings (on cygwin) to allow -Werror" 2008-07-3) was
intended to fix.

In particular, on platforms where the uint32_t type is defined
to be unsigned long, the return type of the new ntohl()/htonl()
is causing gcc to issue printf format warnings, such as:

    warning: long unsigned int format, unsigned int arg (arg 3)

(nine such warnings, covering six different files). The earlier
commit (6e1c234) needed to suppress these same warnings, except
that the types were in the opposite direction; namely the format
specifier ("%u") was 'unsigned int' and the argument type (ie the
return type of ntohl()) was 'long unsigned int' (aka uint32_t).

In order to suppress these warnings, the earlier commit used the
(C99) PRIu32 format specifier, since the definition of this macro
is suitable for use with the uint32_t type on that platform.
This worked because the return type of the (original) platform
ntohl()/htonl() functions was uint32_t.

In order to suppress these warnings, we change the return type of
the new byte swapping functions in the compat/bswap.h header file
from 'unsigned int' to uint32_t.

Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Acked-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Jeff King <peff@peff.net>