Unclear error reporting when running rua inside rua

[vn971]

Steps:

• start installing something, e.g. rua install xcalib
• when reviewing the repo, type T to go to a terminal
• try to run rua from this terminal

Expected at this point: RUA tells you that you're running it inside itself, or fail with some other easy to understand reason

Actual behavior:

thread 'main' panicked at 'Cannot work with PKGDEST environment being set. Please run RUA without it', src/rua_environment.rs:52:2
stack backtrace:
   0: <unknown>
   1: <unknown>

Possible solution: use the already existing mechanism to prevent running multiple instances of RUA simultaneously, before doing other filesystem/environment checks. This will make the error message be something like: Another RUA instance already running. which is arguably more understandable. It is one step from being trivial in that code grouping has to change a little, but that's the only thing that needs to be changed.

Also, it makes sense to remove panicking from the PKGDEST checking code regardless.

[VukoDrakkeinen]

I just tested this on v0.17.4 and rua does exit with Error: another RUA instance already running., so I guess this can be considered fixed already.

[VukoDrakkeinen]

Uh oh, this will also stop subcommands like info and search. Those should be allowed, arguably.

[vn971]

Yeah... Quite unfortunately though.

[vn971]

This got fixed as part of https://github.com/vn971/rua/commit/a56b8863a7ae8c48fd90d477a8c9bb209373ea7b

Because we now take the "uniqueness" lock as early as possible, we also do it before environment checks, which gives an error reason of:

Error: another RUA instance already running.

Hopefully understandable enough for situation of running rua inside rua.