patch 8.0.1782: no simple way to label quickfix entries

Problem:    No simple way to label quickfix entries.
Solution:   Add the "module" item, to be used instead of the file name for
            display purposes. (Martin Szamotulski, closes #1757)

src/alloc.h

@@ -15,6 +15,7 @@ typedef enum {
 	aid_qf_dirname_start,
 	aid_qf_dirname_now,
 	aid_qf_namebuf,
+	aid_qf_module,
 	aid_qf_errmsg,
 	aid_qf_pattern,
 	aid_last