Speed-up phar build process

[mvrhov]

It helps if startBuffering is called when creating a new phar archive.
As the stopBuffering is called I suppose that someone missed the startBuffering directive.

The build times before and after...

time ../box/bin/box build
Building...

real    0m44.691s
user    0m21.601s
sys     0m13.337s

after

time ../box/bin/box build         Building...

real    0m24.135s
user    0m17.877s
sys     0m6.212s

[kherge]

I must have done something wrong since I didn't see any performance difference when I tested the use of that method. Better to have it than not since we all potentially stand to benefit from it!

Thanks!