use of getenv on display mode leads to error

[xdelaruelle]

Some use case of the getenv modulefile command:

set _modules_home [getenv MODULESHOME]
source ${_modules_home}/common

Leads to error when displaying modulefile:

$ module display mod
-------------------------------------------------------------------
/path/to/mod:

Module ERROR: couldn't read file "$MODULESHOME/common": no such file or directory
       while executing
   "source  "${_modules_home}/common"
       (file "/path/to/mod" line 8)
   Please contact <root@localhost>
-------------------------------------------------------------------

On display mode, getenv returns the variable name which leads to such error as the value is expected to fully resolve string value.

[xdelaruelle]

To fix this issue, a --return-value option should be added to the getenv modulefile command to indicate that the value should be returned even on display evaluation mode.

[xdelaruelle]

Same --return-value option should also apply to the getvariant modulefile command.