ENH: Builder loops can now be identified as not "trials" (e.g for blocks)

If a loop represents the stimuli within a trial or blocks around a trial
loop then we don't want it to advance the trialwise data file nor create
new worksheets in the excel file.

Added a parameter `isTrials` to the three loop handlers to flag this
TESTS: added a test for the new option that loops!=trials
TESTS: removed some print statements and making test_info more robust

test_info currently fails if sys.argv[0] is not a valid file which can
occur if
	a) other arguments are on the command call
	b) the argv[0] is a relative path and our cwd has changed
So now we check whether test_info is a valid file path before trying to
use it
Merge pull request #690 from peircej/master

Option to flag a Builder Loop as not being trials (e.g. might be blocks or stimuli)