Move commands.c:cmds_expand_envvars() to utils.c
Rename {cmds_,}expand_envvars() function
Expand environment variables in two options

'fusehome' and 'trashdir'.

Thanks to filterfalse.
Add five unit-tests for expand_envvars() function
Refine utils.c:expand_envvars() function
Correct unit-tests a bit

The purpose of the method was misunderstood.
Don't escape values of envvars for options
Simplify path.c:expand_tilde() a bit
Update docs on envvar expansion for the options

Thanks to filterfalse.
Don't fail with assert on wrong 'trashdir'

Handle this case more gently.  Display errors and don't reset previous
value.
Reject relative path for the 'fusehome' option
Fix several typos in the docs

Thanks to Sebastian Cyprych.
Merge branch 'expand-envvars-in-options'