Changed all of the library tests into actual compile/link tests, to

ensure that the compilation environment is what it needs to be.  Also,
added a test to make sure the C++ compiler has some basic features,
since gcc2.95 will not work.

configure.in

@@ -2,8 +2,8 @@
 # Process this file with autoconf to produce a configure script.
 
 AC_PREREQ(2.59)
-AC_INIT(ledger, 2.1, johnw@newartisans.com)
-AM_INIT_AUTOMAKE(ledger, 2.1)
+AC_INIT(ledger, 2.2, johnw@newartisans.com)
+AM_INIT_AUTOMAKE(ledger, 2.2)
 AC_CONFIG_SRCDIR([main.cc])
 AC_CONFIG_HEADER([acconf.h])
 
@@ -11,12 +11,70 @@ AC_CONFIG_HEADER([acconf.h])
 AC_PROG_CXX
 AC_PROG_MAKE_SET
 AC_PROG_RANLIB
+#AC_PROG_LIBTOOL
+#AM_PROG_LIBTOOL
 
-# Checks for libraries.
-AC_CHECK_LIB([gmp], [__gmpz_add], [],
-  AC_MSG_FAILURE("Could not find gmp (GNU multi-precision) library"))
-AC_CHECK_LIB([pcre], [pcre_compile], [],
-  AC_MSG_FAILURE("Could not find pcre (Perl regular expression) library"))
+# check for C++ compiler compatibility
+AC_CACHE_CHECK(
+  [if C++ compiler is compatible],
+  [cc_compat],
+  [AC_LANG_PUSH(C++)
+   AC_TRY_LINK(
+     [#include <cctype>
+      #include <iostream>],
+     [if (std::isspace(' ') || std::isdigit(' '))
+	std::cout << std::left << std::right << "Hello";],
+     [cc_compat=true],
+     [cc_compat=false])
+   AC_LANG_POP])
+
+if [test x$cc_compat = xfalse ]; then
+  AC_MSG_FAILURE("System's C++ compiler is not compatible (need to use gcc3?)")
+fi
+
+# check for gmp
+AC_CACHE_CHECK(
+  [if libgmp is available],
+  [libgmp_avail],
+  [libgmp_save_libs=$LIBS
+   LIBS="-lgmp $LIBS"
+   AC_LANG_PUSH(C++)
+   AC_TRY_LINK(
+     [#include <gmp.h>],
+     [mpz_t bar;
+      mpz_init(bar);
+      mpz_clear(bar);],
+     [libgmp_avail=true],
+     [libgmp_avail=false])
+   AC_LANG_POP
+   LIBS=$libgmp_save_libs])
+
+if [test x$libgmp_avail = xtrue ]; then
+  AM_CONDITIONAL(HAVE_GMP, true)
+else
+  AC_MSG_FAILURE("Could not find gmp library (set CPPFLAGS and LDFLAGS?)")
+fi
+
+# check for pcre
+AC_CACHE_CHECK(
+  [if libpcre is available],
+  [libpcre_avail],
+  [libpcre_save_libs=$LIBS
+   LIBS="-lpcre $LIBS"
+   AC_LANG_PUSH(C++)
+   AC_TRY_LINK(
+     [#include <pcre.h>],
+     [pcre_free((pcre *)NULL);],
+     [libpcre_avail=true],
+     [libpcre_avail=false])
+   AC_LANG_POP
+   LIBS=$libpcre_save_libs])
+
+if [test x$libpcre_avail = xtrue ]; then
+  AM_CONDITIONAL(HAVE_PCRE, true)
+else
+  AC_MSG_FAILURE("Could not find pcre library (set CPPFLAGS and LDFLAGS?)")
+fi
 
 # check for xmlparse
 AC_ARG_ENABLE(xml,
@@ -35,14 +93,14 @@ if [test x$xml = xtrue ]; then
     [libxmlparse_save_libs=$LIBS
      LIBS="-lxmlparse -lxmltok $LIBS"
      AC_LANG_PUSH(C++)
-     AC_TRY_COMPILE(
-	 [extern "C" {
-	    #include <xmlparse.h>           // expat XML parser
-	  }
-	  class foo {};],
-	 [return 0],
-	 [libxmlparse_avail=true],
-	 [libxmlparse_avail=false])
+     AC_TRY_LINK(
+       [extern "C" {
+	  #include <xmlparse.h>           // expat XML parser
+	}],
+       [XML_Parser parser = XML_ParserCreate(NULL);
+	return parser != NULL;],
+       [libxmlparse_avail=true],
+       [libxmlparse_avail=false])
      AC_LANG_POP
      LIBS=$libxmlparse_save_libs])
   AM_CONDITIONAL(HAVE_XMLPARSE, test x$libxmlparse_avail = xtrue)
@@ -69,7 +127,7 @@ if [test x$python = xtrue ]; then
       [boost_python_save_libs=$LIBS
        LIBS="-lboost_python $LIBS"
        AC_LANG_PUSH(C++)
-       AC_TRY_COMPILE(
+       AC_TRY_LINK(
 	 [#include <boost/python.hpp>
 	  using namespace boost::python;
 	  class foo {};