Clean-up and documentation in processes_select.c

Corrected a Log() message that thought it only related to elapsed
time; it could also relate to other times.  Use isspace() rather
than only comparison to ' ' in case there are tabs.

Made some variables more local, made some comments clearer, added some
comments.  Petty consistency in typography of isspace() calls.

(cherry picked from commit f26442a0129be6514586f641c73ba0da1096fbd1)