remove RT_LWIP_TCP_SND_BUF setting

When not configured in rtconfig.h, lwipopt.h will give us a reasonable
value(TCP_MSS * 2).
Merge pull request #117 from grissiom/fix-sam7x

remove RT_LWIP_TCP_SND_BUF setting
Add device checking when set_device.
remove initialization feature for MS VC++ compiler
fix the spelling wrong
dfs: fix the variable definition bug in copy, found by ffgamelife from rt-thread.org
Merge pull request #120 from prife/dfs-fix

dfs: fix the variable definition bug in copy, found by ffgamelife from rt-thread.org
device: add ref_count support

This is a simple work around to the current device stack design. A
ref_count could let different modules to open/close the same device
independently without interfere others in some degree.

But there is still some data shared between the modules, like flag,
open_flag and user_data. Moreover, it won't yield an error if A open a
device, and B read from it before open it in B. Maybe alloc a new handle
in rt_device_open will be the ultimate solution. But that is much bigger
change and we may leave it to future development.
building.py: add clang static analyzer support

It adds the '--clang-analyzer' option that could invoke clang as the
static code checker. It is recommanded to work with 'scan-build' shipped
with Clang. For example, `scan-build scons --clang-analyzer`.
enhancement hard fault exception handler.
Merge pull request #121 from grissiom/device-ref-count

device: add ref_count support
Merge pull request #122 from grissiom/clang-analyzer

building.py: add clang static analyzer support
Merge pull request #123 from aozima/hardfualt_enhancement

enhancement hard fault exception handler.
Merge pull request #118 from BernardXiong/master

Remove initialization feature for MS VC++ compiler.
fix the memory block splitting issue
add K60Fxxxx bsp for TWR-K60F120M board.
Merge pull request #125 from reynoldxu/K60Fxxxx

add K60Fxxxx bsp for TWR-K60F120M board.
update linker script for components auto initial.
CPPPATH should be string.
update SConstruct.