Work around libiconv failing where there is a more modern version of glibc

libiconv fails to build on ubuntu 14.04 and errors with this without the patch

    In file included from progname.c:26:0:
    ./stdio.h:1010:1: error: 'gets' undeclared here (not in a function)
    _GL_WARN_ON_USE (gets, "gets is a security hole - use fgets instead");
     ^
Add PATH to environment when libiconv is a build dependency
Add PATH to environment when gettext is a build dependency
Merge pull request #318 from jcftang/wip-libiconv-ubuntu1404_glibc_workaround

Work around libiconv failing where there is a more modern version of gli...