[MEDIUM] config: support loading multiple configuration files

We now support up to 10 distinct configuration files. They are
all loaded in the order defined by -f <file1> -f <file2> ...

This can be useful in order to store global, private, public,
etc... configurations in distinct files.
diff --git a/include/common/defaults.h b/include/common/defaults.h
index 9d65f9c..a2267b1 100644
--- a/include/common/defaults.h
+++ b/include/common/defaults.h
@@ -58,6 +58,9 @@
 #define LINESIZE	2048
 #endif
 
+// max # of configuration files
+#define MAX_CFG_FILES   10
+
 // max # args on a configuration line
 #define MAX_LINE_ARGS   64