syslog() should replace %m occurrences in msg with strerror(errno)

[korli]

see ​http://www.opengroup.org/onlinepubs/007908799/xsh/closelog.html

[axeld]

glibc's private strerror_r() was supposed to return a pointer to the string buffer instead of an error code like the POSIX function strerror_r(). glibc's printf() supports "%m" already, and hrev14723 fixes the actual output.

[korli]

tested ok