Fix libpng-1.4 build
fix several translating errors
fix base curve mismatching
update chinese translation
Merge pull request #555 from cherrot/i18n_zh_CN

I18N: Update Chinese translations. Fix several translating errors
High DPI: More fixes, this time cairo stuff

TODO:
 - color picker
 - masks
 - anything else?
Italian translation updated
maybe nitpicky, but I think it's more correct. changed 'and' to 'or'.
added commas, and made some minor wording changes.
edited sentences (and a paragraph break) for clarity.

Some parts in here, I had to reread the text a couple times to make
sure I understood. I think it is clearer the way I've changed it.
Update French translation.
Merge pull request #556 from bartokk/master

Italian translation updated
Lens IOP: add autodetection, based on fact "did user or did not changed anything in GUI from autodetected values"
Merge pull request #548 from LebedevRI/lens-autodetection

Lens IOP: add autodetection
Some more GUI fixes

- Try to keep background grids crisp in custom widgets.
- Put a subdued dt logo into the empty widget of zone system.
Prevent crash on startup. Preliminary fix! I still need to actually reproduce original crash!
https://github.com/darktable-org/darktable/pull/548#issuecomment-42763922
Merge pull request #557 from Terrycloth/clarifying-text-in-user-manual

my first few edits to the user manual.
usermanual: more on tagging (thanks to Christian Kanzian)
Revert "Prevent crash on startup. Preliminary fix! I still need to actually reproduce original crash!"

This reverts commit f6129f8a352dd99037d98d5f8c51680ffb889ada.
Preset update infrastructure: some modules(e.g. lens iop) depend on global data in reload_defaults()

module->init(module); is already called by dt_iop_load_module_by_so()