Block SIGCHLD during select.

Select was losing child termination signals so we explictly
block SIGCHLD during select, and unblock after select returns.
Tested on 256 core smp system, no hangs or zombies.  Thanks
to Alain Miniussi <alain.miniussi@oca.eu> for reporting this.
Fix a dependecy --> dependency comment typo.
Fix error message typo - same named targets with different properties.
Fix dependendency --> dependency comment typo.