Zabbix

 - [ZBX-1020] update default location in manpages;
note in all manpages that absolute path should be used (perviously only agent manpage specified that);
don't claim in the sender manpage that it's the agent;
minor style updates in manpages;
unify help output (capitalisation, style);
reorder help output for agent to match order for other commands;
while at this also :
  note in server manpage that -n does not start server and should be run once only;
  note in sender manpage that proxy should be specified in -z if a host is monitored by a proxy