added --check option to fetchdeps.pl

This checks for any "unexpected" jarfiles - ones not
explicitly downloaded by fetchdeps.pl or explicitly
mentioned in a .gitignore file.

The presence of extraneous jarfiles can cause serious
issues in build artifacts, since the wrong versions
of classes could be included.  (This happened with a
stale version of daemon.jar that caused a deployed
builder to function incorrectly.)
removed redundant target
support uploading of exercises in JSON format

Only course instructors are allowed to do this.
when importing exercise from JSON, ensure that course id is set
set problem authorship/parent hash fields on JSON exercise import

Importing an exercise from JSON data now seems to work.
get rid of an unused import
delta comparison for FP values when testing PYTHON_FUNCTION submissions
whoops, need to "import math" since FP comparison uses math.fabs
ignore /cachedir
Merge branch 'master' into url-page-links