Terrain/RasterRenderer: add "const" keywords
Terrain/RasterRenderer: use Clamp() instead of reimplementing it
Terrain/RasterRenderer: use Clamp() in ClipHeightDelta()
Terrain/RasterRenderer: make "dd2" and "mag" unsigned

Make it a bit more safe against integer overflow and SIGFPE due to
division by zero (TRAC #2613).
Terrain/RasterRenderer: explicitly cast to signed

When multiplying signed*unsigned, the result may be surprising;
explicitly cast to signed to enforce signed multiplication.
Terrain/RasterRenderer: limit height_slope_factor

Limit height_slope_factor so calculating the square of "dd2" will not
overflow.  This avoids calculating the square root of a negative
number, which will then divide by zero (TRAC #2613).
Terrain/RasterRenderer: simplify fudgeelevation formula

Calculate most of it at compile time.
Look/Fonts: Revert the recent font changes for topography labels

This reverts commit 964c3a7485e5a59f291807e090474b826e9c67c8:

An UI regression. Previously topography labels were immediately
obvious simply by looking at the label because of the distinct
rendering in italic. Now you have to scan the surrounding area
to notice the different font size (if it even is sufficiently
different). Even if italic is harder to read (a problem I don't
notice for the labels) this additional scan time will invalidate
the assumed advantages.
InfoBoxWindow: stop dragging before opening dialog

This is necessary on Windows (TRAC #2634).
Terrain/RasterRenderer: add another local variable
Terrain/RasterRenderer: workaround for division by zero

Workaround for TRAC #2613, because I just can't figure this out.
po: update Polish translation
PageActions: rename namespace to "PageActions"
UIGlobals: move ActivateMap() to UIActions.cpp

These are actions that manipulate the user interface, not simple
access to global variables.
Pan: use UIActions and UIGlobals
tools/lk2po.pl: load ENG_MSG.TXT as UTF-8
tools/lk2po.pl: support Vietnamese
tools/lk2po.pl: delete the obsolete menu code

LK8000 menu translations are now in the regular MSG file.
po: add Vietnamese translation

Imported from LK8000.
LanguageGlue: support Vietnamese