class driver can custom string description

some bug fix after the recently merge from simmerge branch

fix memory leak in dfs_elm.c and umount fatfs when mount fatfs fails (this bug leads to mkfs failure in linux)

merge simulator for linux to master branch

fix bug in finsh when built with 64bit-gcc

fixed the string descriptor send to host more than actual

more deterministic on timer

If two timer will timeout at the same tick, the one started later will
be called later. I've tested the patch on simulator and it _seems_ OK.
Reported-by: xdzy on the forum and delin17 <delin17@qq.com>

handle standard request to interface that defined in class

Add RT_MTD_ESRC definitions. If the source page has issue when copying a page, the low level can return this error code. 

remove math code for newlib