MEDIUM: errors: implement parsing context type

Create a parsing_ctx structure. This type is used to store information
about the current file/line parsed. A global context is created and
can be manipulated when haproxy is in STARTING mode. When starting is
over, the context is resetted and should not be accessed anymore.
diff --git a/src/haproxy.c b/src/haproxy.c
index 0e707f5..f4c24ee 100644
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -3380,6 +3380,8 @@
 	}
 
 	global.mode &= ~MODE_STARTING;
+	reset_usermsgs_ctx();
+
 	/*
 	 * That's it : the central polling loop. Run until we stop.
 	 */