Re-raise javac.maxmem to 600m (Fix #10688)
Bump javac.maxmem to 750m
Increase to 1050m

Note: this is the setting for both 32bit and 64bit which
is suboptimal. It may be necessary to create separate
properties for each compile type.
Merge pull request #1080 from joshmoore/javac-64bit-ice34

Re-raise javac.maxmem to 600m (Fix #10688)