Fixes the following GCC 5 warnings:
```
core/io/resource_format_binary.cpp:1721:29: warning: suggest parentheses around arithmetic in operand of '|' [-Wparentheses]
core/typedefs.h:108:24: warning: suggest parentheses around comparison in operand of '!=' [-Wparentheses]
editor/plugins/spatial_editor_plugin.cpp:2202:58: warning: suggest parentheses around comparison in operand of '!=' [-Wparentheses]
editor/plugins/spatial_editor_plugin.cpp:5002:12: warning: suggest explicit braces to avoid ambiguous 'else' [-Wparentheses]
main/input_default.cpp:346:59: warning: suggest parentheses around '-' inside '<<' [-Wparentheses]
main/input_default.cpp:348:60: warning: suggest parentheses around '-' inside '<<' [-Wparentheses]
main/input_default.cpp:579:57: warning: suggest parentheses around '-' inside '<<' [-Wparentheses]
modules/gridmap/grid_map_editor_plugin.cpp:613:14: warning: suggest explicit braces to avoid ambiguous 'else' [-Wparentheses]
modules/theora/video_stream_theora.cpp:335:34: warning: suggest parentheses around '+' in operand of '&' [-Wparentheses]
modules/theora/video_stream_theora.cpp:336:35: warning: suggest parentheses around '+' in operand of '&' [-Wparentheses]
modules/visual_script/visual_script_property_selector.cpp:215:38: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
scene/gui/rich_text_label.cpp:424:84: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
scene/gui/rich_text_label.cpp:512:80: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
scene/gui/scroll_container.cpp:173:36: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
scene/gui/scroll_container.cpp:173:86: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
scene/gui/tree.cpp:1419:98: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
```
We're not formally using C++11 yet so those trigger compilation warnings
(at least with GCC 5):
./main/input_default.h:122:30: warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11
CursorShape default_shape = CURSOR_ARROW;
^
Note: We may allow those eventually (especially for non-int static const),
but most of current occurrences were inconsistent with all other classes.
See also http://www.stroustrup.com/C++11FAQ.html#member-init
The two POSIX style crash handlers (OSX and X11) now remove their signal
handlers when they are destroyed.
Additonally if they are called while no OS singleton is set, they will
simply abort(). This should not happen now that they remove themselves,
but if a future change seperates OS object and crash handler lifetimes,
this may be easier to report/debug than hanging on SIGSEGV.
