exec does not set TERM env when -t passed

Passing -t to docker run will set the TERM environment variable. Doing so to docker exec will not. This causes things like htop to not work.

$ docker run -d --name foo debian bash -c "while true; sleep 1; done"
2fc4a0d2fc6d
$ docker exec -ti foo env
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=2fc4a0d2fc6d

Or a case that the end user is more likely to experience:

$ docker run -d --name foo debian bash -c "while true; sleep 1; done"
2fc4a0d2fc6d
$ docker exec foo "apt-get update && apt-get install -y htop"
....
$ docker exec -ti foo htop
Error opening terminal: unknown.

Versions and stuff:

$ docker version
Client version: 1.3.1
Client API version: 1.15
Go version (client): go1.3.3
Git commit (client): 4e9bbfa
OS/Arch (client): linux/amd64
Server version: 1.3.1
Server API version: 1.15
Go version (server): go1.3.3
Git commit (server): 4e9bbfa
$ uname -a 
Linux hostname 3.13.0-35-generic #62-Ubuntu SMP Fri Aug 15 01:58:42 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
$ docker -D info
Containers: 186
Images: 2828
Storage Driver: aufs
 Root Dir: /var/lib/docker/aufs
 Dirs: 3206
Execution Driver: native-0.2
Kernel Version: 3.13.0-35-generic
Operating System: Ubuntu 14.04.1 LTS
Debug mode (server): false
Debug mode (client): true
Fds: 135
Goroutines: 224
EventsListeners: 1
Init Path: /usr/bin/docker
WARNING: illegal base64 data at input byte 4
WARNING: No swap limit support

Apologies if this has already been reported/fixed (I didn't test against master, even though I know I should!)