This commit consists of numerous small changes, none significant enough to
merit a commit on their own:
* Added extra braces to quash for-loop variable scoping issues for older
compilers (or "g++ -fno-for-scope")
* Appeased "unreachable code" warnings, spurious or otherwise
* Added casts to fix integer-variable signedness warnings
* Added a dummy virtual method to the VectorFileWriter class to silence the
-Wweak-vtables warning from Clang++
* Renamed some parameters in the Expr and GraphicsWindow classes to
eliminate "parameter shadows a field" warnings
* Removed an inert "0 ||" from a conditional, and changed a "&& 0" into an
"#if 0"
* Added missing elements to array/struct/class initializers to zap further
warnings
* Indented some cpp conditionals where appropriate
* Qualified some variables and functions as static to quiet "no previous
declaration" warnings
* toolbar.cpp needed to #include<icons-proto.h> to fix those same "no
previous declaration" warnings from icons.h
* Added some casts and const qualifiers to the Win32 code to address
warnings produced by g++ when compiling under MinGW
* Rewrote Cnf{Freeze,Thaw}Float() to use a union rather than pointer
aliasing; this makes g++ a lot happier
* Removed redundant #includes from win32/w32util.cpp
* With Jonathan's blessing, shortened the last line of the About dialog
text to better match the preceding lines
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