readme: fix debian dependencies

As @bnoordhuis points out, `build-essential` depends on `make` and older
releases call `git` as `git-core`.
Merge pull request #159 from pagespeed/jefftk-debian-dependencies

readme: fix debian dependencies
shutdown-fix: fix a possible crasher on shutdown
Merge pull request #160 from pagespeed/oschaaf-shutdown-fix

shutdown-fix: fix a possible crasher on shutdown
readme: document tengine usage
Merge branch 'master' into oschaaf-statistics
factory-up-front: move driver factory instantiation up front

We need to have the NgxRewriteDriverFactory available at
configuration parse time to set options on it. This change moves
instantiation of the factory in front of configuration parsing.
Afterwards, a check is done to see if we where enabled anywhere.
If we where not enabled / do not have any active server contexts,
the NgxRewriteDriverFactory is deleted. It's not very elegant,
but we can't think of anything better currently.
factory-up-front: style,remove debug code, delay ignore sigpipe call
factory-up-front: fix initialisation
factory-up-front: move comment
Merge branch 'oschaaf-factory-up-front' into oschaaf-statistics

Conflicts:
	src/ngx_pagespeed.cc
	src/ngx_rewrite_driver_factory.cc