Resolve failures with the POSIX sem implementation of APR
process mutexes (and thus global mutexes) in environments which
receive signals.

EINTR is now handled on the sem_* calls that are documented as
exposing EINTR in the Linux, FreeBSD, and/or Solaris docs.

There are a few other calls that haven't been updated: 
sem_unlink(), sem_post(), and sem_close().


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/trunk@1610854 13f79535-47bb-0310-9956-ffa450edef68