preEnv in main not stack safe (probably scala stream issue)

[siddhartha-gadgil]

When running on the exported file for group.lean in sbt, I get a stack overflow, which (as running in console shows) is in defining the preEnv. A hack that worked once is to add .toVector to exported commands, i.e., modify to

val exportedCommands = TextExportParser.parseFile(opts.inputFile).toVector

but crashes are random and may be some problem with my setup.