Clarify port forwarding sections

Fixed a line that I think was misplaced and expanded a bit the section "Port forwarding on steroid".
Increasing the number of open files by docker process.
Merge pull request #461 from SvenDowideit/amend-durdns-workaround-patch

Clarify port forwarding sections
Ensure network is up before starting ntpclient, sets and locks the system clock
Set default docker files limits.
Renaming ulimit env variable
Merge pull request #468 from boot2docker/fixclock

Fix the system clock sync
Merge pull request #466 from azukiapp/increasing_files

Increasing the number of open files by docker process.
Fix several issues with our init script

- replace `"` with `'` as appropriate
- allow `DOCKER_DIR` to be configured via "/var/lib/boot2docker/profile"
- add `DOCKER_LOGFILE` variable to control where the daemon logs go, and switch them from overwrite to append
Output from "ping" is distracting and irrelevant

... especially on QEMU, where we can't ping out, so it just prints to the console endlessly
Merge pull request #471 from tianon/init-issues

Fix several issues with our init script
Merge pull request #472 from tianon/ping-output

Output from "ping" is distracting and irrelevant
Speed up ssh access by turning off DNS checking