cmd/go: another attempt at flag handling for coverage
The -cover flag is now just enable/disable and is implied if
either of the other flags is set.

R=rsc
CC=golang-dev
https://codereview.appspot.com/10420043
crypto/tls: change advertised ciphersuite order.

TLS clients send ciphersuites in preference order (most prefereable
first). This change alters the order so that ECDHE comes before plain
RSA, and RC4 comes before AES (because of the Lucky13 attack).

This is unlikely to have much effect: as a server, the code uses the
client's ciphersuite order by default and, as a client, the non-Go
server probably imposes its order.

R=golang-dev, r, raggi, jsing
CC=golang-dev
https://codereview.appspot.com/10372045
cmd/go: document that files beginning with . or _ are ignored

Fixes issue 5655.

R=golang-dev, minux.ma, r
CC=golang-dev
https://codereview.appspot.com/10410045
test: match gccgo error messages

R=iant, golang-dev
CC=golang-dev
https://codereview.appspot.com/10365052
find external tools in $PATH
Merge branch 'master' into gitfix