fix: adhoc files should not pick up default lean version from open folder

[lovettchris]

fixes #227

[Vtec234]

Hm, could we ask Elan for what the default version is instead, and then use the 'select Lean toolchain' machinery to run that? I guess this will work but it's a bit complicated to make a temp folder just because the Lean version is selected based on cwd.

[lovettchris]

Hm, could we ask Elan for what the default version is instead, and then use the 'select Lean toolchain' machinery to run that? I guess this will work but it's a bit complicated to make a temp folder just because the Lean version is selected based on cwd.

@Vtec234 - done. It now forces adhoc files to use the elan default toolchain, with the side effect that if there is no default it installs the nightly build as the new default.

[Vtec234]

Thanks!