Add .vagrant to .gitignore
Switch Vagrant Box to precise32.
Fix typo in doc string of ebib-format-fields.
Reverse fields when saving a .bib file.

This commit undoes f5e0e9e6c0933345509f4f193dd47781afc7a7c6 and does the
reversing of fields within an entry when saving, rather than loading.
This requires only one call to `reverse', instead of using append.