Fixed the --with-zlib configure option so that it always adds the specified

path to the compiler flags.  Before, a zlib installation in the default
path was always used in preference to the one in the desired location.

configure.ac

@@ -941,27 +941,35 @@ dnl Check for & handle argument to --with-zlib.
 
 _cppflags=$CPPFLAGS
 _ldflags=$LDFLAGS
-OPT_ZLIB="/usr/local"
 AC_ARG_WITH(zlib,
 AC_HELP_STRING([--with-zlib=PATH],[search for zlib in PATH])
 AC_HELP_STRING([--without-zlib],[disable use of zlib]),
                [OPT_ZLIB="$withval"])
 
-case "$OPT_ZLIB" in
-  no)
-    AC_MSG_WARN([zlib disabled]) ;;
-  *)
+if test "$OPT_ZLIB" = "no" ; then
+    AC_MSG_WARN([zlib disabled])
+else
+  if test "$OPT_ZLIB" = "yes" ; then
+     OPT_ZLIB=""
+  fi
+
+  if test -z "$OPT_ZLIB" ; then
     dnl check for the lib first without setting any new path, since many
     dnl people have it in the default path
 
     AC_CHECK_LIB(z, inflateEnd,
                    dnl libz found, set the variable
                    [HAVE_LIBZ="1"],
-                   dnl if no lib found, try to add the given library
-                   [if test -d "$OPT_ZLIB"; then
+                   dnl if no lib found, try /usr/local
+                   [OPT_ZLIB="/usr/local"])
+
+  fi
+
+  dnl Add a nonempty path to the compiler flags
+  if test -n "$OPT_ZLIB"; then
      CPPFLAGS="$CPPFLAGS -I$OPT_ZLIB/include"
      LDFLAGS="$LDFLAGS -L$OPT_ZLIB/lib$libsuff"
-                   fi])
+  fi
 
   AC_CHECK_HEADER(zlib.h,
     [
@@ -1004,8 +1012,7 @@ case "$OPT_ZLIB" in
     AC_MSG_NOTICE([found both libz and libz.h header])
     curl_zlib_msg="enabled"
   fi
-    ;;
-esac
+fi
 
 dnl set variable for use in automakefile(s)
 AM_CONDITIONAL(HAVE_LIBZ, test x"$AMFIXLIB" = x1)