merge backout

Backed out changeset 3d54cf97598d (see issue916 for details)

i18n, record: improve use of translated docstring in prompts The old code would confuse the user if the translator actually translated the letters "Ynsfdaq?" in the prompt, since the user input would be matched against the English string, despite the translation. The new code fixes this, but the translator must be 100% consistent. Also, the translation of single character strings is problematic if they are used differently by different pieces of code.

i18n: use gettext instead of _ Both gettext and _ trigger a translation at runtime, but _ can only be used with a string argument since it also triggers string extraction.

i18n: mark help strings for translation The gettext function is just another name for the normal _ function and it is used for translating docstrings when using _ would make pygettext.py output a warning.

restructure helptable When looking up a help topic, the key is now only matched against the short names for each topic, and not the header. So hg help 'Environment Variables' must be replaced with hg help env

Do not try to load extensions twice (issue811)

enhance the error output in case of failure during http push

tag: without a checkout, base the tag changeset on tip instead of nullid issue916

use Exception(args)-style raising consistently (py3k compatibility)