MISC: Fix typo s/Adlib/AdLib/ (only where visible to the user)
GUI: Fix description of game specific extraPath
SWORD1: Change "no DXA support" message.

It's "without zlib" or "without DXA support". WJP prefers the first.
GUI: change FullScreen into fullscreen

This makes it consistant with other references to fullscreen.
GRAPHICS: Fix some Doxygen comments that seem wrong.
COMMON: Fix some Doxygen comments that seem wrong.
BACKENDS: Fix some Doxygen comments that seem wrong.
ENGINES: Fix some Doxygen comments that seem wrong.
GUI: Fix some Doxygen comments that seem wrong.
AUDIO: Fix some Doxygen comments that seem wrong.
WINTERMUTE: Remove unused Sqr-function.
Merge pull request #493 from BenCastricum/branch2

MISC: Some minor typo fixes
Merge pull request #495 from somaen/docuFix

Doxygen-fixes
I18N: Update credits for Dutch translation
I18N: Update scummvm.pot from source
I18N: Add Dutch translation