openssh: Make ControlMaster feature work

The ControlMaster feature for multiplexing used hard links, which
does not work on Android starting in Android 6.0. Replace this
with a non-atomic check-then-rename for now. Fixes #91.

packages/openssh/build.sh

@@ -1,7 +1,7 @@
 TERMUX_PKG_HOMEPAGE=http://www.openssh.com/
 TERMUX_PKG_DESCRIPTION="Secure shell for logging into a remote machine"
 TERMUX_PKG_VERSION=7.1
-TERMUX_PKG_BUILD_REVISION=1
+TERMUX_PKG_BUILD_REVISION=2
 TERMUX_PKG_SRCURL=http://ftp.eu.openbsd.org/pub/OpenBSD/OpenSSH/portable/openssh-${TERMUX_PKG_VERSION}p1.tar.gz
 TERMUX_PKG_DEPENDS="libandroid-support, ldns, openssl"
 # --disable-strip to prevent host "install" command to use "-s", which won't work for target binaries:

packages/openssh/mux.c.patch

@@ -0,0 +1,34 @@
+diff -u -r ../openssh-7.1p1/mux.c ./mux.c
+--- ../openssh-7.1p1/mux.c	2015-08-21 00:49:03.000000000 -0400
++++ ./mux.c	2015-12-17 19:20:36.368902909 -0500
+@@ -1295,6 +1295,22 @@
+ 	}
+ 
+ 	/* Now atomically "move" the mux socket into position */
++#ifdef __ANDROID__
++	/* Android does not support hard links, so use a non-atomic
++	   check-then-rename for now. */
++	if (access(orig_control_path, F_OK) == 0) {
++		error("ControlSocket %s already exists, disabling multiplexing",
++		    orig_control_path);
++		unlink(options.control_path);
++		goto disable_mux_master;
++	} else {
++		if (rename(options.control_path, orig_control_path) == -1) {
++			fatal("%s: link mux listener %s => %s: %s", __func__, 
++			    options.control_path, orig_control_path,
++			    strerror(errno));
++		}
++	}
++#else
+ 	if (link(options.control_path, orig_control_path) != 0) {
+ 		if (errno != EEXIST) {
+ 			fatal("%s: link mux listener %s => %s: %s", __func__, 
+@@ -1307,6 +1324,7 @@
+ 		goto disable_mux_master;
+ 	}
+ 	unlink(options.control_path);
++#endif
+ 	free(options.control_path);
+ 	options.control_path = orig_control_path;
+