Deactivate multi-thread in multi-dex mode

It should already have been the case, but it wasn't and it crashed.

Change-Id: Icb461d6e43ef2d113f59038d8c2327f3cfaff86c
(cherry picked from commit cf069ca52f2af9f70fcbeac99443f00401d43b4a)
Fix BufferOverflowException when merging dexes

Bug: 11519714

The bug was due to the fact that when merging 2 dexes, not enough size may be reserved for the "typeLists" section.
This is because we only aligned the sum of the size of both sections.
If both typeLists sections were aligned with 2 and not with 4, we are 4 bytes short when writing.

Change-Id: I73b51eb25434a622143011741a69b88d42507f43
(cherry picked from commit 2241dbe132cf90b58f93c014bdd807405b7f82f5)
Changed dvmDexCacheStatus to check for odex file first.

This prevents the generation of a new dexfile when an odex file already
exists when switching between Art and Dalvik.

Bug: 13463154
Change-Id: I55ef9abe1fe172ee656550e78556381f95698c33