MMC/SD Card Subsystem

Some changes to the MMC/SD card subsystem
o update library 
o SDHC support
o read-only mode
o long file names (VFAT)
o clean separation of menuconfig settings
o fine-grained debug level
o  EMCD commands separately selectable
o  new commands "info" and "rm"
o fix bug #92 (bugs.ethersex.de)