tmac: rename IM (italic manual) to MR (manual reference)

Suggested by G. Brandon Robinson.

man/man4/smugfs.4

@@ -24,7 +24,7 @@ is a user-level file system that provides access to images
 stored on the SmugMug photo sharing service.
 It logs in after
 obtaining a password from 
-.IM factotum (4)
+.MR factotum (4)
 using
 .B server=smugmug.com
 and
@@ -32,7 +32,7 @@ and
 (if any)
 as key criteria
 (see
-.IM auth (3) ).
+.MR auth (3) ).
 Then 
 .I smugfs
 serves a virtual directory tree mounted at
@@ -265,7 +265,7 @@ SmugMug,
 If multiple categories or albums have the same name,
 only one will be accessible via the file system interface.
 Renaming the accessible one via Unix's
-.IM mv (1)
+.MR mv (1)
 will resolve the problem.
 .PP
 Boolean values appear as