mktemp improvements

- add -p dir, -t and -u.
- fix dirname(tmp) check (did not check null terminator).

the semantics of mktemp is now the same as OpenBSD mktemp.

mktemp.1

@@ -1,4 +1,4 @@
-.Dd January 31, 2015
+.Dd May 8, 2015
 .Dt MKTEMP 1
 .Os sbase
 .Sh NAME
@@ -6,7 +6,8 @@
 .Nd create temporary file or directory
 .Sh SYNOPSIS
 .Nm
-.Op Fl dq
+.Op Fl dqtu
+.Op Fl p Ar directory
 .Op Ar template
 .Sh DESCRIPTION
 .Nm
@@ -20,8 +21,25 @@ tmpdir set to '/tmp' or, if set, the TMPDIR environment variable.
 .Bl -tag -width Ds
 .It Fl d
 Create a temporary directory instead of a file.
+.It Fl p Ar directory
+Use the specified
+.Ar directory
+as a prefix when generating the temporary filename. The directory will be
+overridden by the user's
+.Ev TMPDIR
+environment variable if it is set. This option implies the
+.Fl t
+flag (see below).
 .It Fl q
 Fail silently if an error occurs.
+.It Fl t
+Generate a path rooted in a temporary directory.
+.It Fl u
+Unlink file before
+.Nm
+exits. This is slightly better than
+.Xr mktemp 3
+but still introduces a race condition. Use of this option is not encouraged.
 .El
 .Sh SEE ALSO
 .Xr mkdtemp 3 ,