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 |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- init.c
+++ init.c	2016-07-26 12:03:14.963958298 +0000
@@ -3330,8 +3330,8 @@ void mutt_init (int skip_sys_rc, LIST *c
     MailcapPath = safe_strdup (p);
   else
   {
-    /* Default search path from RFC1524 */
-    MailcapPath = safe_strdup ("~/.mailcap:" PKGDATADIR "/mailcap:" SYSCONFDIR "/mailcap:/etc/mailcap:/usr/etc/mailcap:/usr/local/etc/mailcap");
+    /* Default search path from RFC1524 plus fallback for mutt specific defaults */
+    MailcapPath = safe_strdup ("~/.mailcap:" PKGDATADIR "/mailcap:" SYSCONFDIR "/mailcap:/etc/mailcap:/usr/etc/mailcap:/usr/local/etc/mailcap:" SYSCONFDIR "/mutt/mailcap");
   }
 
   Tempdir = safe_strdup ((p = getenv ("TMPDIR")) ? p : "/tmp");