The problemBag is confusing (with respect to multiple problems being
loaded), because it seems as though it is reloaded each time, making
each draw random rather than shuffled. Here is a proposed alternative,
based solely on the problemNum. If it’s not really important to be
precise with the weighting (that ouf of 10 draws, something with
probability .30 is chosen exactly three times), the last three lines
can be replaced with `problem = problems.eq(Math.floor(Math.random() *
typeIndex.length));` Otherwise, the ‘jostler’ substitutes for the
shuffle, preventing it from going in the sequential order except when
the weightSum is a mulitple of three. There probably are some slight
improvements that could be made, because when there are only two
equally weighted exercises, they alternate every time. One idea is to
duplicate the array if it is below some minimum length and than shuffle
according to a seed (so that it is deterministic). But it’s not clear
to me that this differs drastically from actual randomness.

Incompatible with:
- data-weight=“0”
- data-weight=“0.6” (permutations_1, permutations_and_combinations_2)
Change incompatible exercises; allow for data-weight="0"

- Changed all exercises with `data-weight` equal to some decimal.
- Deleted some exercises with `data-weight=“0”`
- Some exercises with `data-weight=“0”` used it as a template to reduce
redundancy. Since this is clever, I added the one line neccessary to
allow it.
- Deleted (inferior) alternative method that was commented out
- Included `id = $(problem).attr(“id”)` which was an oversight to not
be included the first time around.
- Changed `else if` to `else` because there should be no cases where
`typeof exerciseId === undefined` or `problems.length === 0`.
Fix problemId (to work without name) and 4-space indents (sorry)

Silly editor; tabs are for kids.
hide arrowAtClipPoint
Make inscribed polygons exercise more lenient
Add extra domain requirement when dividing by x
Remove assumption in question
Add getClockwiseCoords to MovableAngle for interactive-graph angle grading

Test Plan:
 * test.html add in interactive-graph
 * add an angle
 * try grading with the coordinates in both positions
   (normal and flipped, but with the angle measure correct)

Auditors: alex, eater
Merge pull request #156673 from petercollingridge/constructions2

Make inscribed polygons exercise more lenient
Merge pull request #156705 from petercollingridge/sim-rat-exp-4

Add domain requirement to simplifying rational expressions 4 when needed
correct hint, fix #156972

move negative sign to the numerator
Merge pull request #157558 from mauk81/patch-4

correct hint, fix #156972
Merge pull request #155599 from mauk81/improve

hide arrowAtClipPoint
Add a message on "Check Answer" when empty

Summary:
Displays "It looks like you haven't answered all of the question yet."
to the student if they click "Check Answer" without having filled out
all of the question.

Hopefully this reduces the number of confused students who think the
website is broken (and the number of bug reports sent for not filling
in the whole question).

Test Plan:
 * python -m SimpleHTTPServer 7000
 * visit http://localhost:7000/exercises/factoring_linear_binomials.html
 * press "Check Answer" without filling anything out
 * answer the question and make sure it still works

Reviewers: eater

Reviewed By: eater

CC: alpert, alex

Differential Revision: http://phabricator.khanacademy.org/D5898
subkatex
Fix setting parseError in calculator

Summary:
Taken from D5922 until it's decided what to do with that.  Previously
the code was attempting to set an error handler which would allow the
calculator to catch any parse errors, since that was not set correctly,
any parsing errors (such as "(") cause a javascript error and scroll the
page to the top.

Test Plan:
* open an exercise with a calculator (like standard deviation)
* put some malformed input in, like 'sqrt(', hit enter
* the calculator should output 'err' and there shouldn't be a javascript error.

Auditors: alex
adjust calculator tests
Update kas.js
Merge pull request #159247 from mauk81/fixTests

adjust calculator tests
Merge pull request #159367 from mauk81/patch-4

Update compiled version of kas.js