Upgrade qtip plugin for jQuery.

Resolves "jQuery.browser is deprecated" message when you hover over "Acceptable
formats".

Test Plan:
Hover over Acceptable Formats in Square Roots 2, locally, Chrome/OS X

Auditors: eater, alpert
make startLoadingExercise available to the outside via Khan so that assessments can access the promise of the exercise html file having been loaded

Test Plan:
go to an assessment
add breakpoint in makeProblem
make sure that the old problem isn't shown yet

Reviewers: alpert

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D2089
Merge branch 'arcpatch-D2089'
Fix coin_flip_sequences post-jQuery 1.9

Test plan: local/chrome

fix #42553; fix #42526; fix #42518; fix #42500; fix #42493; fix #42488;
fix #42486; fix #42480; fix #42471; fix #42470; fix #42452; fix #42450;
fix #42433; fix #42411; fix #42407; fix #42147;

Auditors: alpert
Emit to stderr every time we process a new file.

Summary:
If we're processing a bunch of files on stdin, it will say:
   processing exercise -
a lot, but it's better than nothing: at least we know it's working.
And when you list files on the commandline, the output will actually
be useful!

Test Plan:
Ran 'make exercises' and observed proper output:
   ... packing exercise rotation_of_polygons.html
   ... packing exercise rounding_numbers.html
   ... packing exercise rounding_whole_numbers.html
   ... packing exercise same_side_exterior_angles.html
   ... packing exercise same_side_exterior_angles_2.html
   <etc>

Reviewers: alpert, eater

Reviewed By: eater

Differential Revision: http://phabricator.khanacademy.org/D2092
Remove @ from the xpath expression in Plotting the Line of Best Fit.

Test Plan:
locally, Chrome/OS X

Auditors: eater, alpert
Merge branch 'master' of github.com:Khan/khan-exercises
Remove extraneous solution element from square_roots_2

What in the world?!?

Test plan: local/chrome

fix #42567; fix #42552; fix #42539; fix #42517; fix #42516; fix #42515;
fix #42506; fix #42504; fix #42483; fix #42428; fix #42425; fix #42424;
fix #42421; fix #42409; fix #42406

Auditors: alpert
Fix hint in balancing_checmical_equations

Test plan: local

Auditors: alpert
Correctly handle ^1 in expressions.js

Test plan:
Verify question is displayed correctly in http://localhost:8000/exercises/simplifying_expressions_with_exponents.html?seed=6&problem=simplify-exponential-form-mini&debug

fix #42543; fix #42484; fix #42482; fix #42455; fix #42391; fix #42365;
fix #42361; fix #42326; fix #42316; fix #42312; fix #42276; fix #42257;
fix #42241

Auditors: alpert
Correctly avoid unanswerable questions :(

Test plan:
http://localhost:8000/exercises/powers_of_complex_numbers_1.html?debug&problem=0&seed=180
http://localhost:8000/exercises/powers_of_complex_numbers_1.html?seed=193&problem=0&debug

fix #42619; fix #42614; fix #42612; fix #42609; fix #42608; fix #42606;
fix #42598; fix #42562; fix #42561; fix #42554; fix #42532; fix #42530;
fix #42524; fix #42508; fix #42501; fix #42492; fix #42489

Auditors: alpert
Avoid unanswerable questions here too

cf. http://www.reddit.com/r/Khan/comments/19zclt/

Auditors: eater
Disable scratchpad for Brit's interactive exercises

Test plan: local

fix #42751; fix #42604; fix #42596; fix #42594; fix #42578; fix #42229;
fix #42921; fix #42098; fix #42069

Auditors: alpert
Accept the correct answer for the nonlinear case in plotting_the_line_of_best_fit

Test plan: local

fix #43060; fix #43059; fix #43058; fix #43057; fix #43052; fix #43050;
fix #43049; fix #43048; fix #43046; fix #43044; fix #43041; fix #43037;
fix #43012; fix #43010; fix #43009; fix #43003; fix #43000; fix #42999;
fix #42998; fix #42997; fix #42995; fix #42994; fix #42993; fix #42992;
fix #42991; fix #42990; fix #42988; fix #42986; fix #42980; fix #42979;
fix #42977; fix #42974; fix #42972; fix #42971; fix #42970; fix #42969;
fix #42968; fix #42967; fix #42964; fix #42962; fix #42960; fix #42959;
fix #42958; fix #42956; fix #42953; fix #42952; fix #42949; fix #42948;
fix #42947; fix #42946; fix #42945; fix #42943; fix #42941; fix #42937;
fix #42936; fix #42935; fix #42934; fix #42932; fix #42931; fix #42929;
fix #42927; fix #42925; fix #42920; fix #42917; fix #42915; fix #42912;
fix #42911; fix #42909; fix #42908; fix #42907; fix #42902; fix #42899;
fix #42898; fix #42896; fix #42891; fix #42890; fix #42886; fix #42884;
fix #42882; fix #42880; fix #42878; fix #42875; fix #42874; fix #42873;
fix #42872; fix #42866; fix #42864; fix #42863; fix #42859; fix #42856;
fix #42854; fix #42852; fix #42851; fix #42850; fix #42849; fix #42847;
fix #42843; fix #42842; fix #42841; fix #42840; fix #42839; fix #42837;
fix #42835; fix #42833; fix #42830; fix #42827; fix #42825; fix #42824;
fix #42822; fix #42821; fix #42809; fix #42808; fix #42806; fix #42805;
fix #42802; fix #42801; fix #42798; fix #42796; fix #42794; fix #42787;
fix #42785; fix #42784; fix #42780; fix #42778; fix #42773; fix #42770;
fix #42768; fix #42763; fix #42762; fix #42760; fix #42753; fix #42747;
fix #42746; fix #42743; fix #42741

Auditors: cbhl
Returned my version of powers of complex numbers to normal
Merge branch 'master' of https://github.com/Khan/khan-exercises