decided against using XXX in the manual for unknown versions
add noreturn attr on Fatal()
refactor some of the output mtime-handling code

Reduces duplicated explain output.
Improved bash completion when using tools like '-t clean'
Merge pull request #526 from RedX2501/improved_bash_completion

Improved bash completion when using tools like '-t clean'
fix compile error about noreturn on windows
Merge pull request #527 from wang-bin/compile_fix

fix compile error about noreturn on windows
move test virtual time "now_" into VirtualFileSystem

It's the only piece that cares about the current time.
split FakeCommandRunner out of BuildTest

Separating concerns to make a subsequent refactoring easier.
sync version number in master with release

Update RELEASING with notes on how to not screw this up again.
add DepsLog, a new data structure for dependency information

DepsLog is a compact serialization of dependency information.
It can be used to replace depfiles for faster loading.
pass command results via a struct

WaitForCommand now passes all command output via a struct.
This will allow adding more output in a future change.
factor out implicit dep loading
use DepsLog in loading dependencies

WIP
factor out creation of build directory
load deps log at startup
no error if deps log doesn't exist
plumb DepsLog load through Builder
expand DepsLog test, fix two bugs it revealed
track deps log load time in metrics