gnustep-gui and /proc

[Sergei Gnezdov]

While installing gnustep-gui I faced an error message:

  gnustep-gui requres procfs mounted to build or run.

I think that error message should give some instructions how to
proceed.  It could be nice to warn about security implications as
well.

Makefile diff:

51c51
< IGNORE=               requires procfs mounted to build or run
---
> IGNORE=       requires procfs mounted to build or run.  Mount command: 'mount_procfs proc /proc'.  To mount /proc during startup modify /etc/fstab to contain: 'proc /proc procfs rw 0 0'.