Fix compile errors with gcc 4.3

amount.cc

@@ -4,6 +4,7 @@
 #include <list>
 #include <sstream>
 #include <cstdlib>
+#include <memory>
 
 #include <gmp.h>
 

datetime.cc

@@ -7,6 +7,7 @@
 
 #include <ctime>
 #include <cctype>
+#include <climits>
 
 date_t       date_t::now(std::time(NULL));
 int	     date_t::current_year = date_t::now.year();

textual.cc

@@ -19,6 +19,7 @@
 #include <cctype>
 #include <cstdio>
 #include <cstdlib>
+#include <climits>
 
 #ifdef HAVE_REALPATH
 extern "C" char *realpath(const char *, char resolved_path[]);