Looks like the 1.5.3 configure script inadvertently dropped support for alternate cURL library path support via --with-libcurl:
Yes, because it's the crappy way to do it. The right way is to export a variable to specify the PKG_CONFIG_PATH to the correct *.pc file. See my RPMs for reference...
Seems to be a way that works on more systems and with local built binaries is the right way to do it. Dependance on a packaging system is the crappy way to do it.