Implement 3 new functions:

Implement 3 new functions:
	- g_lcm() - calculates Least Common Multiple of two given values,
		it is helpful when we need to find sector size for provider
		which is based on disks with different sector size;
	- g_get_mediasize() - returns media size of given provider;
	- g_get_sectorsize() - returns sector size of given provider;
Those function aren't used now, but are used by geom_mirror which will be
committed soon.