read /usr/share/mutt/mailcap as fallback by default. This allows to
set some useful defaults specifically for mutt. For example
text/html
Index: mutt-1.5.21/init.c
===================================================================
---
 init.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- init.c
+++ init.c	2017-04-28 13:44:54.680745977 +0000
@@ -3935,7 +3935,8 @@ void mutt_init(int skip_sys_rc, LIST *co
     /* Default search path from RFC1524 */
     MailcapPath = safe_strdup(
         "~/.mailcap:" PKGDATADIR "/mailcap:" SYSCONFDIR
-        "/mailcap:/etc/mailcap:/usr/etc/mailcap:/usr/local/etc/mailcap");
+        "/mailcap:/etc/mailcap:/usr/etc/mailcap:/usr/local/etc/mailcap"
+	SYSCONFDIR "/mutt/mailcap");
   }
 
   Tempdir = safe_strdup((p = getenv("TMPDIR")) ? p : "/tmp");