fix the .dir-locals.el file

... so that it sets coq-prog-name just locally in the current buffer.
Otherwise its value can spoil coq projects in other buffers visiting
files in other directories that must be used with another version of
coqtop.
fix the .dir-locals.el file, part 2 (oops)

... so that it sets coq-prog-name just locally in the current buffer.
Otherwise its value can spoil coq projects in other buffers visiting
files in other directories that must be used with another version of
coqtop.
Merge pull request #306 from DanGrayson/fix-dir-locals

Fix dir locals