buildin variables in repo forall command

repo forall 內建幾個環境變數，讓你方便作 每個 project 的操作。
用 repo help forall 就會列出：

---

Environment
-----------
pwd is the project's working directory. If the current client is a
mirror client, then pwd is the Git repository.

REPO_PROJECT is set to the unique name of the project.

REPO_PATH is the path relative the the root of the client.

REPO_REMOTE is the name of the remote system from the manifest.

REPO_LREV is the name of the revision from the manifest, translated to a
local tracking branch. If you need to pass the manifest revision to a
locally executed git command, use REPO_LREV.

REPO_RREV is the name of the revision from the manifest, exactly as
written in the manifest.

shell positional arguments ($1, $2, .., $#) are set to any arguments
following <command>.

Unless -p is used, stdin, stdout, stderr are inherited from the terminal
and are not redirected.

---

所以要在 android project 中，把所有 project 都加入一個 remote target ，可以用 repo forall -c 'git remote add mynb ssh://checkonb/home/checko/androidcode/$REPO_PATH' 這是把nb 上的 android source 加到自己的 remote 中。
要使用 repo 內建環境變數， forall -c 後面的 command，要用小字串符號括起來 ' '，這樣 repo 才會正確轉換 $NAME 為變數內容。

可以用
repo forall -c 'echo $REPO_PROJECT $REPO_PATH' 看一下變數的內容

REPO_LREV : local revision (commit)
REPO_RREV : remote revision/branch 

因為 repo sync 只會 checkout revision 出來，不會順變 checkout -b branchname，所以可以用

repo forall -c 'git checkout -b $REPO_RREV'

然後用 repo status 就可以看每個 project 的 branch name ..