Decrease default -Xmx to 512 MB for 32-bit versions

Setting this too high (especially on Windows, where address space is
limited to 2GB) often results in insufficient memory to run
acquisitions.

Keeping the 768 MB default for OS X 32-bit, since OS X 32-bit apps have
a 4 GB address space.

git-svn-id: https://valelab.ucsf.edu/svn/micromanager2/trunk@14728 d0ab736e-dc22-4aeb-8dc9-08def0aa14fd
Lift direct buffer memory limit on OS X

Do the same as already done on Windows. This prevents out of memory
errors when acquiring to RAM that until now occurred long before actual
system memory is exhausted.

git-svn-id: https://valelab.ucsf.edu/svn/micromanager2/trunk@14729 d0ab736e-dc22-4aeb-8dc9-08def0aa14fd