This allows users to write Bash commands like:
guix time-machine -C <(echo %default-channels) -- ...
or:
guix build -m <(echo '(specifications->manifest (list "guile"))')
Previously, on GNU/Linux, they would fail with:
error: failed to load '/dev/fd/63': No such file or directory
* guix/ui.scm (try-canonicalize-path): New procedure.
(load*): Use it.
* tests/guix-build.sh: Test 'guix build -m' with a /dev/fd/N file.