update clipper to 5.1.0-svn and adjust to new PolyTree API
Merge maurerpe's threaded printer control code from his fork

This replaces libreprap
(GH-88)
printer: Include sys/types.h for ssize_t on Debian
obey autoconf warning about modernize AM_INIT_AUTOMAKE
check for installed clipper lib

(GH-86)
win32: Bump libsigc++ dependency. Improve Cross-Compile doc

Older libsigc++ doesn't build with newer MingW headers, but the
latest one does and is compatible.

Update the WIN32_CROSS_COMPILE.txt to note that the gcc-mingw32
variant of MingW successfully compiles things that work these
days.
amf-tools: Fix compilation on win32 with newer MingW

stdio.h is the correct header to include on any platform to get
fopen and friends.
clipper: Add a constructor for PolyNode.

Missing constructor for the PolyNode class leads to uninitialised
pointer use in some cases.

Filed upstream as http://sourceforge.net/p/polyclipping/bugs/64/
geometry: Silence a compiler warning due to dangling code.

Code below the final return statement in fit_arc() was leading to
a compiler warning about reaching the end of a non-void function.
Comment it out.
simplify settings by removing double definition of names

glade widget is now found only by member name
-> don't distinguish between settings in and not in glade ui
  -> don't warn anymore when a setting is not found in glade
- rename "RGBA" settings to "Colour" for reading settings from existing
  config
version 2.2.0
clipper update to 5.1.3-svn
fix clipper's new API adaptation of PolyTree to ExPoly conversion

using the author's suggestion
brute-force attempt on finding display font

and don't crash when no font is found
(GH-90)
actually try fonts if found and even try courier

(GH-90)
fix mutex lock-unlock sequence typo

causing segfault on freebsd since glib 2.32
Merge remote-tracking branch 'upstream/master'
Clipper workaround to prevent hangs during slicing