patchbomb: Hoist sender config higher.

Automated merge with http://hg.intevation.org/mercurial/crew

patchbomb: Validate email config before we start prompting for info.

Introduce find_exe. Use instead of find_in_path for programs. The behaviour of find_in_path was broken for config options containing path names, because it always searched the given path, even when not necessary. The find_exe function is more polite: if the name passed to it contains a path component, it just returns it.

ui: Rename has_config to has_section.

patchbomb: Defer the import of readline. If imported at the top of the module, the import appears to succeed, but raw_input doesn't acquire magic editing fu. I suspect this has something to do with the newish demandimport code, because the prior code worked with demandload.

patchbomb: Don't prompt for headers until sure we have revs to export. The prior behaviour was to always prompt for headers, and only then bomb out if there were actually no revs to send.

wsgicgi: change stdin to binary mode

Also check the index file size when deciding whether to reload a revlog. This should fix some spurious failures from test-clone-pull-corruption (issue552).

use .extend instead of .append in readtags