Lower warning to allow building with gcc
Lower warnings to fix build with gcc
Fix the following -Werror warnings from clang 3.5.0, while building
usr.sbin/rtadvd:

usr.sbin/rtadvd/rtadvd.c:1291:7: error: taking the absolute value of unsigned type 'unsigned int' has no effect [-Werror,-Wabsolute-value]
                    abs(preferred_time - pfx->pfx_pltimeexpire) > rai->rai_clockskew) {
                    ^
usr.sbin/rtadvd/rtadvd.c:1291:7: note: remove the call to 'abs' since unsigned values cannot be negative
                    abs(preferred_time - pfx->pfx_pltimeexpire) > rai->rai_clockskew) {
                    ^~~
usr.sbin/rtadvd/rtadvd.c:1324:7: error: taking the absolute value of unsigned type 'unsigned int' has no effect [-Werror,-Wabsolute-value]
                    abs(valid_time - pfx->pfx_vltimeexpire) > rai->rai_clockskew) {
                    ^
usr.sbin/rtadvd/rtadvd.c:1324:7: note: remove the call to 'abs' since unsigned values cannot be negative
                    abs(valid_time - pfx->pfx_vltimeexpire) > rai->rai_clockskew) {
                    ^~~
2 errors generated.

These warnings occur because both preferred_time and pfx_pltimeexpire
are uint32_t's, so the subtraction expression is also unsigned, and
calling abs() is a no-op.

However, the intention was to look at the absolute difference between
the two unsigned quantities.  Introduce a small static function to
clarify what we're doing, and call that instead.

Reviewed by:	hrs
MFC after:	3 days
Differential Revision: https://reviews.freebsd.org/D1197
sh: Prepend "$0: " to error messages if there is no command name.
Fix the following -Werror warnings from clang 3.5.0, while building
bsnmpd's snmp_hostres module:

usr.sbin/bsnmpd/modules/snmp_hostres/hostres_snmp.c:204:20: error: absolute value function 'abs' given an argument of type 'const long' but has parameter of type 'int' which may cause truncation of value [-Werror,-Wabsolute-value]
        str[9] = (u_char)(abs(tm->tm_gmtoff) / 3600);
                          ^
usr.sbin/bsnmpd/modules/snmp_hostres/hostres_snmp.c:204:20: note: use function 'labs' instead
        str[9] = (u_char)(abs(tm->tm_gmtoff) / 3600);
                          ^~~
                          labs
usr.sbin/bsnmpd/modules/snmp_hostres/hostres_snmp.c:205:22: error: absolute value function 'abs' given an argument of type 'const long' but has parameter of type 'int' which may cause truncation of value [-Werror,-Wabsolute-value]
        str[10] = (u_char)((abs(tm->tm_gmtoff) % 3600) / 60);
                            ^
usr.sbin/bsnmpd/modules/snmp_hostres/hostres_snmp.c:205:22: note: use function 'labs' instead
        str[10] = (u_char)((abs(tm->tm_gmtoff) % 3600) / 60);
                            ^~~
                            labs

Since tm::tm_gmtoff is a long, use labs(3) instead.

MFC after:	3 days
Change man(1) to use mandoc to render manpages

man(1) now first test the manpage to run with mandoc to make sure it can be
rendered.
In case groff cannot be found (because base has been built WITHOUT_GROFF) it
recommands to install groff from the packages
Fix typo
filedesc: plug a test for impossible condition in fgetvp_rights
Fix comments
Include required files directly instead of pollution via ufs/ufsmount.h.

Sponsored by:	Nginx, Inc.
buf.h is not needed here, and pollutes when ufsmount.h is included
from userland code.

Sponsored by:	Nginx, Inc.
ifdef RACCT ui_racct_foreach and struct uidinfo's ui_racct

Change racct_ create and destroy to macros evaluating to nothing without RACCT
so that their callers passing ui_racct don't have to be ifdefed.
Do not include buf.h.
Merge from projects/sendfile:

o Provide a new VOP_GETPAGES_ASYNC(), which works like VOP_GETPAGES(), but
  doesn't sleep. It returns immediately, and will execute the I/O done handler
  function that must be supplied as argument.
o Provide VOP_GETPAGES_ASYNC() for the FFS, which uses vnode_pager.
o Extend pagertab to support pgo_getpages_async method, and implement this
  method for vnode_pager.

Reviewed by:	kib
Tested by:	pho
Sponsored by:	Netflix
Sponsored by:	Nginx, Inc.
Don't use the synchronization endpoint unless referenced by the
isochronous endpoint descriptor used for the data transfers, hence the
synchronization feature might not be supposed to be supported [yet].
This makes seamless playback synced with the USB HOST clock work with
the DN32-USB module for Midas audio systems and possibly other similar
products from Klark Teknik.

MFC after:	1 week
Fix the following -Werror warning from clang 3.5.0, while building the
ath kernel module:

sys/dev/ath/ath_hal/ar5212/ar5212_reset.c:2642:7: error: taking the absolute value of unsigned type 'unsigned int' has no effect [-Werror,-Wabsolute-value]
                if (abs(lp[0] * EEP_SCALE - target) < EEP_DELTA) {
                    ^
sys/dev/ath/ah_osdep.h:74:18: note: expanded from macro 'abs'
#define abs(_a)         __builtin_abs(_a)
                        ^
sys/dev/ath/ath_hal/ar5212/ar5212_reset.c:2642:7: note: remove the call to '__builtin_abs' since unsigned values cannot be negative
sys/dev/ath/ah_osdep.h:74:18: note: expanded from macro 'abs'
#define abs(_a)         __builtin_abs(_a)
                        ^
1 error generated.

This warning occurs because both lp[0] and target are unsigned, so the
subtraction expression is also unsigned, and calling abs() is a no-op.

However, the intention was to look at the absolute difference between
the two unsigned quantities.  Introduce a small static function to
clarify what we're doing, and call that instead.

Reviewed by:	adrian
MFC after:	3 days
Differential Revision: https://reviews.freebsd.org/D1212
\n at end of panicstr is redundant.

Submitted by:	alc
Consider the negation operator (!) to be a word even if it is not followed
by whitespace.  This allows "optional !foo" which is what most programmers
are naturally going to tend to do as opposed to "optional ! foo".
Misc mdoc fixes:

- Remove superfluous paragraph macros.
- Remove/fix empty or incorrect macros.
- Sort sections into conventional order.
- Terminate quoted strings properly.
- Remove EOL whitespace.
Squelch a (bogus) used before init warning when building with gcc.