To provide typing and auto-completion information, we create a
background process by starting lean with the option --server.
In "server" mode, we create snapshots of the parser state.
The idea is to be able to quickly reprocess a file when the user makes a
modification. This commit fixes a bug in the snapshot operation.
It was not saving in the snapshots the unique name generator used by the parser.
By creating a fresh name generator, we may accidentally
assign the same internal name to two different constants.
This bug triggered the crash described in issue #593.
This commit fixes the test in the comment
https://github.com/leanprover/lean/issues/593#issuecomment-101768484
This commit also adds a smaller version of the problem to the test suite
11fbee269b