Reintroduce BOARD_VOLD_EMMC_SHARES_DEV_MAJOR

Code taken from CM7's vold

Conflicts:
	Android.mk
vold: add ro.vold.umsdirtyratio property

This allows control of what /proc/sys/vm/dirty_ratio is used when USB mounting.
Some platforms like the HTC Desire (bravo) get a _HUGE_ performance boost when
writing to the sdcard when USB mounting if this is set to 20 (which is the default)
on the HTC Desire.

This addresses this issue: http://code.google.com/p/cyanogenmod/issues/detail?id=2949

Basicly it makes it possible to undo or control the effect of this commit:
https://github.com/CyanogenMod/android_system_vold/commit/a28056b38275003895ff5d9576681aca01544822

Change-Id: I86b7bbd02695fb0c19f39448714a219257bf806f
DirectVolume: handle discs with multiple major numbers

CFlag: BOARD_VOLD_DISC_HAS_MULTIPLE_MAJORS

Allows Direct Volume to handle discs with multiple major numbers.
Needed on Samsung Galaxy S II and variants.

For example:
mmcblk0p1 - 179:0
mmcblk0p2 - 179:1
mmcblk0p3 - 179:2
mmcblk0p4 - 256:0
mmcblk0p5 - 256:1

Change-Id: I633ac882a721cde25f0df779b4028efa6be15750
vold: fix an offset one bug that makes partition 4 unusable

Change-Id: Ic8e18e6191ad7ee33162e36060b57a6802cf0883