Environment: FreeBSD 9.1-RELEASE i386

During a libcurl-related debugging exercise following an upgrade from
2.0.19 to 2.0.20, I discovered that configure was not finding and using
the installed /usr/local/bin/curl-config. I was passing
--with-libcurl=/usr/local to configure. config.log was showing failure
to discover curl-config but success finding libcurl:

configure:9445: checking for /usr/local/bin/curl-config
configure:9478: result: no
configure:9595: checking whether libcurl is usable
configure:9628: cc -o conftest -O -pipe -march=pentium4 -I/usr/local/include

-I/usr/local/include -L/usr/local/lib conftest.c -L/usr/local/lib -lcurl >&5

  configure:9628: $? = 0
  configure:9642: result: yes

Passing a bare --with-libcurl to configure worked:

  
  configure:9486: checking for curl-config
  configure:9504: found /usr/local/bin/curl-config
  configure:9516: result: /usr/local/bin/curl-config
  configure:9527: checking for the version of libcurl
  configure:9534: result: 7.24.0
  configure:9541: checking for libcurl >= version 7.10
  configure:9554: result: yes

Looking at the configure script, it was passing a fully-qualified
pathname for curl-config (instead of just the program name) to
AC_PATH_PROG, which will never work. The attached patch against the
STABLE-BRANCH-2-0 m4/libcurl.m4 yields what I believe to be the intended
result:

configure:9522: checking for the version of libcurl
configure:9529: result: 7.24.0
configure:9536: checking for libcurl >= version 7.10
configure:9549: result: yes