RFR:7199207 Placeholders cleanup

[Karen Kinnear]

Please review:
http://cr.openjdk.java.net/~acorn/7199207.fix2merge/webrev/

bug: NPG: Crash in PlaceholderTable::verify, after a StackOverflow during class loading
https://jbs.oracle.com/bugs/browse/JDK-7199207

Thanks to Stefan Karlsson for the initial analysis and the test case.

Thanks to Coleen's suggestion, I've simplified the placeholder table entry cleanup.
Specifically the placeholder table is not used to keep the instanceKlass alive for GC during class resolution, and no
other logic depends on the contents of the placeholder table. Therefore rather than retaining the entries for the entire
span of resolve_from , entries are explicitly added and removed for each specific resolution action: LOAD_INSTANCE,
LOAD_SUPER and DEFINE_CLASS (used for parallel class loading).

Tests run:
Original test case from bug (linux 32 bit client)
regression tests on solaris/sparc 32 bit:
  vm.sysdict.testlist
  vm.quick.testlist
  vm.parallel_class_loading.testlist: no flags, -XX:+AllowParallelDefineClass, -XX:+UnsyncLoadClass, -XX:+PrintSystemDictionaryAtExit
  java.lang.instrument: jtreg
  jli with -Xcomp
  ctw nightly.testlist
tests in progress on solaris/sparc 32 bit:
  runThese -Xcomp
  jck vm

thanks,
Karen