print.gtable: print z order but don't sort names by z order

Previously, the layout names were sorted by z order, but the grobs weren't.
This resulted in a mismatch between the names and the grobs. It's better
to not sort by z by default, since that doesn't match how indexing works.
Update NEWS
Fix visual test for new version of vtest
Merge pull request #35 from wch/print-order

Fixes to print order
Add NEWS header
print.table: fixes to documentation for R CMD check
Update version
Add plyr to suggests, for tests
Merge tag 'gtable-0.1.2'
merged changes from upstream into my fork