add gcc.ld to bsp/simulator
add .gdbinit to bsp/simulator
fix memory leak in dfs_elm.c and umount fatfs when mount fatfs fails (this bug leads to mkfs failure in linux)
add sd_erase in sd_sim.c, just erase MBR in SDCARD
just mask signal in sdl_fb.c
fix memory leak in sd_erase in bsp/simulator
Merge pull request #20 from prife/simmerge

some bug fix after the recently merge from simmerge branch