add less_than_int, greater_than_int to edify

Add functions less_than_int() and greater_than_int() that interpret
their args as ints and do the comparison.  ("<" and ">" operators, if
implemented, should do string comparison.)  This lets us do the build
time check currently done by the check_prereq binary.
diff --git a/edify/main.c b/edify/main.c
index 03eefc6..0e36108 100644
--- a/edify/main.c
+++ b/edify/main.c
@@ -143,6 +143,16 @@
     expect("if \"\" then yes endif", "", &errors);
     expect("if \"\"; t then yes endif", "yes", &errors);
 
+    // numeric comparisons
+    expect("less_than_int(3, 14)", "t", &errors);
+    expect("less_than_int(14, 3)", "", &errors);
+    expect("less_than_int(x, 3)", "", &errors);
+    expect("less_than_int(3, x)", "", &errors);
+    expect("greater_than_int(3, 14)", "", &errors);
+    expect("greater_than_int(14, 3)", "t", &errors);
+    expect("greater_than_int(x, 3)", "", &errors);
+    expect("greater_than_int(3, x)", "", &errors);
+
     printf("\n");
 
     return errors;