Add function to retrieve rpm config base directory

- one-shot to determine configuration base directory path from
  RPM_CONFIGDIR environement or build-time default
- rpmfileutil is a bit strange place, this would really belong to librpm
  but Lua initialization needs the path so...

rpmio/macro.c

@@ -1630,4 +1630,3 @@ rpmExpandNumeric(const char *arg)
 
     return rc;
 }
-

rpmio/rpmfileutil.c

@@ -25,6 +25,8 @@
 
 #include "debug.h"
 
+static const char *rpm_config_dir = NULL;
+
 static int open_dso(const char * path, pid_t * pidp, rpm_loff_t *fsizep)
 {
     static const char * cmd = NULL;
@@ -727,3 +729,12 @@ int rpmMkdirs(const char *root, const char *pathstr)
     argvFree(dirs);
     return rc;
 }
+
+const char *rpmConfigDir(void)
+{
+    if (rpm_config_dir == NULL) {
+	char *rpmenv = getenv("RPM_CONFIGDIR");
+	rpm_config_dir = rpmenv ? xstrdup(rpmenv) : RPMCONFIGDIR;
+    }
+    return rpm_config_dir;
+}

rpmio/rpmmacro.h

@@ -137,6 +137,17 @@ char * rpmExpand	(const char * arg, ...) RPM_GNUC_NULL_TERMINATED;
  */
 int	rpmExpandNumeric (const char * arg);
 
+/** \ingroup rpmmacro
+ * Return rpm configuration base directory.
+ * If RPM_CONFIGDIR environment variable is set, it's value will be used.
+ * Otherwise the configuration directory is the one set at build time,
+ * typically /usr/lib/rpm. The value of rpmConfigDir() is determined
+ * on first call to this function and is guaranteed to remain the same
+ * on subsequent calls.
+ * @return		rpm configuration directory name
+ */
+const char *rpmConfigDir(void);
+
 #ifdef __cplusplus
 }
 #endif