fix memleak in WebPIDelete()

happens when decoding is partial (past Partition0), without error and
interrupted by calling WebPIDelete()

WebPIDelete() needs to call VP8ExitCritical() to free in-flight resources

Change-Id: Id4faef1b92f7edd8c17d642c58860e70dd570506
(cherry picked from commit 40ae3520b19e9f2ed22d52b7677d846da8da90de)
libwebp.jar: build w/Java 1.6 for Android compat

broken since:
 a5c297c swig/java: reduce wrapper function code duplication

this was a part of v0.3.1, but not v0.3.0.

Change-Id: I001d4bd0a7a1aa1b2d267bc63bc1d8226bff00c1
(cherry picked from commit de899516c752faab0bfe87eb6614e7960022809f)