Compressed LCP and Compressed Backup (and switching them on/off online)

Quick experiment with online changing of enabling/disabling compressed backups and local checkpoints (LCPs).

Backup is incredibly trivial and correct (even have some nodes do compressed, some not).

LCPs are a bit trickier when it comes to restore… currently how the code sits is that a block using the compressed file interface in NDBFS must specify if it wants to use the compressed read/write interface or not. So when you have LCPs that differ in compressed/non-compressed than the current config file setting, you’re not going to be able to restore them (although setting CompressedLCP=1 should let you restore either compressed or non-compressed LCPs).

At some point, I’ll probably move AsyncFile (our async file IO class) to just use azio alway, and modify azio to be transparent for non-compressed files…. I just have to fix up azio for direct io.