testbench: string: make delayed_faulting_echo() slightly clearer

Also, move call_ping() into a different function and stop using the (absent)
reset label for syncing.
ipc: clean up misleading comments

Also some redundant TRACE()s.
testbench: add getpid() to testbench, forkserv

process.c actually keeps a cached value in task_pid, rather than calling to
the pager each time. The technical reason is that this lets me use "fuck"
another time in a serious computer program.
testbench: account for the "exited, not joined" condition

It was only relevant because of the assert, and its effective postcondition
necessitates a call to abs(). You may shed a tear for the test environment's
micro-efficiency now.
testbench: add ipc suite, test of anylocalthread receive

Predictably, it hits the panic() call in ipc_recv_half, which was stubbed out
by changing the parameter to anythread. This causes the test to fail, and so
all is well.
testbench: string: remove todo from finite_xfer_timeout

It passes. The test isn't very good, but so far it passes.