Failing test for suggested_payment of 0

This means we annoy non-active users, which we don't want to do!
Fix bug in suggested_payment
Use suggested_payment in support-gittip template
Merge pull request #2658 from gittip/stop-being-annoying

stop annoying non-active users
Bump version to 15.0.11
Bump version to 15.0.11-dev
fall back to English when translation string is empty
add a Makefile target that extracts i18n messages
don't use interpolation so the messages can be automatically extracted
use a syntax for plurals that works with automatic message extraction
ran `make i18n_update`
blank out missing translations
turn off fuzzy matching
finish wrapping messages for i18n in `templates/base.html`
complete the i18n of four templates
wrap the messages in `templates/support-gittip.html` for i18n
remove trailing zeros
use "$" instead of "$US" as the USD symbol in French
make i18n_update