strerror is not threadsafe, replace with fr_syserror

fr_syserror uses TLS to create a thread local buffer, and calls strerror_r to write out the value.
Only skip on vendor if were searching for a callback
More configuration sanity checks for rlm_ldap
Move setting of packet->timestamp
Set fake packet timestamp from request packet timestamp
localtime_r can return NULL on error, we should probably check that
Output to collectd