Request for reviews (XS): 7180769: assert(tboth->klass_is_exact()) failed: klass should be exact

[Vladimir Kozlov]

http://cr.openjdk.java.net/~kvn/7180769/webrev

7180769: assert(tboth->klass_is_exact()) failed: klass should be exact

Regression after 7170463 changes. Result of join() with interface class produces 
non-exact type:

tcon: precise klass java/lang/String: 0x0000000111a57dd8:Constant:exact *
tval: Interface:klass org/apache/derby/iapi/store/raw/xact/TransactionId: 
0x00000001174cc278 *
obj_type: org/apache/derby/iapi/store/raw/xact/TransactionId:NotNull *
tboth: org/apache/derby/iapi/store/raw/xact/TransactionId:NotNull *

Use class exactness as part of the condition for class compare optimization 
instead of assert.

Tested with failed test.

Thanks,
Vladimir