R: use brewed gettext
R: use brewed gettext

On clean install, update.packages() was failing with:
In file included from R_systat.c:23:
./foreign.h:33:10: fatal error: 'libintl.h' file not found

Closes #676.

goxberry/homebrew-science,ge11232002/homebrew-science,quantumsteve/homebrew-science,dpo/homebrew-science,ahundt/homebrew-science,kozo2/homebrew-science,philippbayer/homebrew-science,andrewjpage/homebrew-science,pditommaso/homebrew-science,heuermh/homebrew-science,aeantipov/homebrew-science,pmelsted/homebrew-science,DabeDotCom/homebrew-science,joshbode/homebrew-science,parcollet/homebrew-science,maplesond/homebrew-science