Configure: fixed perl Makefile generation (ticket #334). Dependancy tracking introduced in r5169 were not handled absolute path names properly. Absolute names might appear in CORE_DEPS if --with-openssl or --with-pcre configure arguments are used to build OpenSSL/PCRE libraries. Additionally, revert part of r5169 to set NGX_INCS from Makefile variables. Makefile variables have $ngx_include_opt in them, which might result in wrong include paths being used. As a side effect, this also restores build with --with-http_perl_module and --without-http at the same time.