dx.bat: Don't change directory.

Changing directory to that of dx.bat prevents dx.bat from being
used with relative directories. This leads to all sorts of
issues integrating it with build systems that expect this to
work.

I've tested that this change works under the following conditions:
1. Android SDK in a path containing spaces.
2. java.exe in a path containing spaces.
3. Java object files in a path containing spaces.
4. Output jar file in a path containing spaces.
5. Java object files specified with relative paths.
6. Java object files specified with absolute paths.
7. Output jar file specified with relative paths.
8. Output jar file specified with absolute paths.

Change-Id: I1b47a6cc73169607cc6238acf197e3b467c9bcbc
Implement the dalvik side of libcore.reflect.

(Cherry-pick of b4d5cf78d4731ffc6211d07a0d69c92c559ba792.)

Change-Id: I5d1b41f029c9c49a2d60a066a5fb0ed0f52f4b52
Merge "dx.bat: Don't change directory."
Merge "Implement the dalvik side of libcore.reflect."
Minor code cleanup to address warnings found by Clang.

cherry-picked from internal Android branch
55617c82a73d84ff3695bdd5526159448262d009

Change-Id: I0f78ca6b8293c13d7dbb535556543f6ea9f4dd45
Merge "Minor code cleanup to address warnings found by Clang."
Merge branch 'master' of https://android.googlesource.com/platform/dalvik into jb-devel