addon/validation: Rename addon_name_legal() to addon_filename_legal()

Conflicts:
	src/tests/test_addons.cpp
campaignd: Restrict possible add-on name chars to a whitelist

The check is intentionally separate from the filenames check now.

The new whitelist includes all alphanumerical characters,
hyphen-minuses -, and underlines _ ([A-Za-z0-9_-]).

Conflicts:
	src/addon/validation.cpp
	src/tests/test_addons.cpp
campaignd: Allow existing add-ons with invalid names to be reuploaded

This change is for backwards compatibility purposes only in order to
allow authors to continue uploading new versions of add-ons with
previously valid names that have been rendered invalid by the whitelist
addon_name_legal() method. This commit should be reverted next time an
add-ons server instance is deployed (hopefully for 1.12 first instead of
1.13.x).

A warning is provided in the logs for admins whenever an add-on with an
invalid name is reuploaded.
Handle boost::iostreams::gzip_error in the SDL_net-based network layer

(part of bug #20205)

The exception in question originated from the read_gz() call and caused
the entire process to abort because of a non-fatal issue occurring in a
secondary thread.

First spotted in campaignd. See the bug report for details.

Conflicts:
	changelog
Fix bug #20205

Malformed data caused config::error exception to be thrown.

Unfortunately campaignd on catching such an exception had no way to
close the right connection, instead all connections were closed because
the local variable that was supposed to contain connection number wasn't
updated. This is fixed by using boost.exception to attach the necessary
data to config::error objects so it can be used at the catch site.
Brainfart fix
updated French translation
Make travis a bit less verbose
campaignd: Mention name rule changes in the changelog
fixed broken about.cfg entry spottet by wmlling (thanks shadowmaster)
Fix a compiler warning.
Fix a compiler warning.
updated Scottish Gaelic translation
Test for "mandatory" WML child, fixing bug #20852.

This bug does not exist in trunk, due to the major refactoring
that has been done to gamestatus.cpp.
Don't strip underscores from keys when trying to remove a translation mark

Backported from master a1e5070ab6bddcaa2d607e60c944d9c68e40ad2b
updated Japanese translation
pot-update (reference update only, no new/changed strings)
fix # wmllint: deathcheck off directive being ignored in some cases
remove files on Windows so --revert and second conversions can proceed

Windows won't allow a rename to overwrite an existing file (Error 183, file already exists).
miscellaneous spelling corrections