using File::Which to defensively avoid invoking executables that aren't installed
Merge pull request #23 from dginev/defensive_system_calls

 using File::Which to defensively avoid invoking executables that aren't...
 More robust testing when kpsewhich isn't present
 fix pathname lookup logic to always precede kpsewhich with pathname_find
 meaningful comment on the TeX pathanme_find lookup
 skipped tests always announce themselves. latexmlc invocation is now a little more portable
 adding requirements for all TeX-dependent tests
Merge pull request #24 from dginev/skip_tests_on_missing_TeX

 More robust testing without a TeX installation
 never try socket connections without latexmls installed
 sort keys of attributes for LaTeXML::Post::Document::addNodes processing
 wrap kpsewhich in quotes to handle Windows unescaped spaces as returned by which()
 math attributes now ordered alphabetically, regenerating test files
careful not to overwrite manually set box sizes
tweaked the fake box dimensions
added a pxValue method to dimensions
careful about inheritting non-LaTeXML attributes to math nodes
use pxValue instead of ptValue for pixels; add missing \fi
updated tests for tweaked box sizing
added \tracingcommands; refactored conditionals to better modularize code and to better support tracing
adjustments to DefConditional to combine all conditionals, elses, etc