manpath issues a warning if MANPATH is already set; ignore it
manpath issues a warning if MANPATH is already set; ignore it

Broken mostly recently by daa2c94.

Asuza/App-perlbrew,Asuza/App-perlbrew,ptolemarch/App-perlbrew,josl/App-perlbrew,rafl/App-perlbrew,calid/App-perlbrew,Asuza/App-perlbrew,calid/App-perlbrew,josl/App-perlbrew,rafl/App-perlbrew,josl/App-perlbrew,rafl/App-perlbrew,ptolemarch/App-perlbrew,ptolemarch/App-perlbrew