Harmonized strptime() with GNU R

GNU R's implementation of strptime() ignores trailing
characters after the format string.

That is,
strptime("2012-12-31 adfasdfsdf", "%Y-%m-%d")

evaluates to "2012-12-31"
[zoo package] Fixed handling of zero-length symbols
[zoo package] Removed graphics-related stubs from maven test runner

This was causing problems because it set the environment of plot() to
the empty environment rather than the graphics namespace. we have
since stubbed out plot() in the graphics package anyway
Merge pull request #20 from billy1380/master

Fixes #19: Take into account ignoreLines argument in scan()
- changed scan test to include more variety in txt file (added column headings)
- added empty string and case insensitive NA and boolean detection