Provide better message for bad tests/env

We provide a nice error message when you `make run` with a bad
local.env, but `make test` with a bad tests/env was giving just
SystemExit. This commit subclasses SystemExit to provide a more
specific error message.
Made robots.txt disallow crawling any JSON at all.
Merge pull request #1785 from duckinator/robots.txt-simplification

Made robots.txt disallow crawling any JSON at all.
Merge pull request #1784 from gittip/bad-envvar-tests

Provide better message for bad tests/env
Add JSONP support to charts.json
Merge pull request #1790 from gittip/issue-1715

Add JSONP support to charts.json
Bump version to 10.2.2
Bump version to 10.2.2-dev
Fixed #1789 -- Removed text 'lurking' to friendlier text.

Changed "user is lurking" to "user is quietly watching the Gittip world".
JS cleanup
fix tip validation error for HTML5 browsers

while it's convenient to automatically add/remove in 25 cent
increments, the HTML5 spec says that if you provide a step value, any
values between those steps are considered invalid
shorten tip input fields
Corrected the stats page link
Merge pull request #1792 from onceuponatimeforever/1789

Fixed #1789 -- Removed text 'lurking' to friendlier text.
Merge pull request #1796 from yasoob/patch-1

Corrected the stats page link
#1754: better keyboard controls for tipping

Now:
+ pushing enter submits your change
+ pushing escape cancels the change
+ when the user starts typing and then pauses for 1 second, the input
is validated again (enabling the "confirm" button)
Note Fundly on the README
Bump version to 10.2.3
Bump version to 10.2.3-dev
properly check bounds to prevent UI bug

In the two browsers I checked (Firefox and Safari), pressing return to
close the JS alert (for an invalid/out-of-bounds tip) re-triggers tip
submission since the tip input field is still focused. Before this
commit I worked around that by focusing on the confirm/cancel links,
but this adds a proper solution by doing bounds checking.