Squashed commit of the following:
sched: Rename all use of system_t to clock_t.
syscall: Rename all use of system_t to clock_t.
net: Rename all use of system_t to clock_t.
libs: Rename all use of system_t to clock_t.
fs: Rename all use of system_t to clock_t.
drivers: Rename all use of system_t to clock_t.
arch: Rename all use of system_t to clock_t.
include: Remove definition of systime_t; rename all use of system_t to clock_t.
Change all calls to mq_receive() and mq_timedreceive() in the OS to calls to nxmq_receive() and nxmq_timedreceive(), making appropriate changes for differences in return values.
sched/mqueue: Add nxmq_receive() and mxmq_timedreceive() which are functionally equivalent to the standard mq_receive and mq_timedreceive() except that (1) they do not create cancellation points, and (2) the do not modify the application's errno variable.
Change all calls to mq_send() and mq_timedsend() in the OS to calls to nxmq_send() and nxmq_timedsend(), making appropriate changes for differences in return values.
sched/mqueue: Add internal function nxmq_send() and nxmq_timedsend() that are equivalent to mq_send() and mq_timedsend() except that they do not create cancellation points and do to not modify the errno variable.
sched/mqueue: Rename all private static functions for use the nxmq_ vs. mq_ naming.
sched/mqueue: Rename all OS internal functions declared in sched/mqueue/mqueue.h to begin with nxmq_ vs. mq_. The mq_ prefix is reserved for standard application interfaces.
This is analogous to similar renaming that was done previously for semaphores.
Squashed commit of the following:
sched/signal: Fix a few compile warnings introduced by naming changes.
sched/signal: Rename all private, internal signl functions to use the nxsig_ prefix.
sched/signal: Rename sig_removependingsignal, sig_unmaskpendingsignal, and sig_mqnotempty to nxsig_remove_pendingsignal, nxsig_unmask_pendingsignal, and nxsig_mqnotempty to make it clear that these are OS internal interfaces.
sched/signal: Rename sig_findaction and sig_lowest to nxsig_find_action and nxsig_lowest to make it clear that these are OS internal interfaces.
sched/signal: Rename sig_allocatepingsigaction and sig_deliver to nxsig_alloc_pendingsigaction and nxsig_deliver to make it clear that these are OS internal interfaces.
sched/signal: Rename sig_cleanup, sig_release, sig_releasependingaction, and sig_releasependingsignal to nxsig_cleanup, nxsig_release, nxsig_release_pendingaction, and nxsig_release_pendingsignal to make it clear that these are OS internal interfaces.
sched/signal: Rename sig_tcbdispatch and sig_dispatch to nxsig_tcbdispatch and nxsig_dispatch to make it clear that these are OS internal interfaces.
sched/signal: Rename sig_releaseaction and sig_pendingset to nxsig_release_action and nxsig_pendingset to make it clear that these are OS internal interfaces.
sched/signal: Rename sig_initialize and sig_allocateactionblock to nxsig_initialize and nxsig_alloc_actionblock to make it clear that these are OS internal interfaces.
