voms-proxy-destroy does not respect X509_USER_PROXY environment variable

[jolange]

When setting the X509_USER_PROXY environment variable, voms-proxy-init and voms-proxy-info respect that as the default location, i.e. you don't have to specify the file parameter.

$ export X509_USER_PROXY=$PWD/tmp_proxy_file
$ voms-proxy-init
Created proxy in <PWD>/tmp_proxy_file.
$ voms-proxy-info
...
path      : <PWD>/tmp_proxy_file
timeleft  : 11:59:26
...

voms-proxy-destroy does not use that environment variable, though:

$ voms-proxy-destroy
Proxy file doesn't exist or has bad permissions

You have to specify a file parameter here, if you don't use the default location.

Is this intended for some reason? Otherwise I'd have a "fix" ready, which I could submit.