Moved vim-relevant lines to its own section in main .gitignore
Ignoring vim backup (~) files
Ignoring gcov and gcov2perl automatically generated files

These files turn up when one runs 'make cover' and don't need to be in the
output from 'git status'
Ignoring html files generated by 'cover' in 'make cover'
Merge pull request #948 from paultcochrane/ptc/gitignore_extras

Ignore more automatically generated files in .gitignore