Add --bwlimit option to sxcp
Check if bandwith limit is set before trying to distribute it over hosts. Fix for bb #510.

Add debugging entries to functions responsible for bandwindth limit
setting and getting.
Use usleep() call as fallback when curl_multi_wait() returns immediately

Increase usleep() timeout when curl_multi_wait() returns and if it
happens more than 2 times in a row, fall asleep for consequently longer
timeouts, but less than maximal value (100ms).
Fix debug message.
Cosmetic changes.
CHECKPOINT_RESTART when idle, and auto-checkpoint in blockmgr/jobmgr
fix error path leak