Write to correct xmp file when manually writing

this was broken for duplicates
Bump db version to 2: write_timestamp
Update write_timestamp when writing xmp file
Add a crawler that checks all xmp files on start
lua : api, enable external formating functions

this should solve most of the problems of wiki vs usermanual syntax
lua : always expand path name before importing a directory
change dt_film_cleanup to not always destroy empty films.

lua needs to create empty films
lua : add a function to create an empty film

dt.films.new("directory"):dt_lua_film_t
Fix typo in preference defintion.
Merge pull request #431 from hean01/master

Fix typo in preference defintion.
Fix a typo.
Fix a typo.
Fix left out rename of capture module to tethering while initializing view manager.
Merge pull request #432 from hean01/master

A few fixes.
Merge branch 'usermanual'

This brings the usermanual to version 1.4.1 (not directly related to the darktable version):

* finally we pass xmllint
* pretty printing of docbook sources
* very few typo fixes and style improvements

This breaks the usermanual string freeze and was aligned beforehand with the active manual translators.
Deflicker: prerequired changes to the core

1. We need to know original(uncorrected) black level and white point from raw image.
2. We need a way to modify histogram precision - 64 bins is definetly not enough.
Raw black point/white level: libraw path
Put raw black level/white point into image cache
Mark some missing files for translation

... and remove others that no longer exists
opencl: add 'GeForce 9400 GT' (with that spelling) to nvidia_gpus.h fixes #9777