drivers/enc28j60: Dead code removal

Removed bunch of commented-out code and unused function in the enc28j60 driver.
drivers/enc28j60: Rename driver symbols

Change driver symbol names to match style used in core driver.
drivers/enc28j60: Removed enc28j60conf.h

The file was containing unneeded constant renames.
drivers/enc28j60: Created CS assert and release macros

Defined macros enc28j60_release_cs() and enc28j60_release_cs() and replaced all
manual bit clear/set with them.
drivers/enc28j60: Removed #include global-conf.h

The enc28j60.c and network.c no longer include global-conf.h. This is a step
needed to rewrite build system. Configuration variables should be injected
using the '-include' command line parameter to gcc.
uip: Removed #include uip-conf.h

This is another step on a way to rewrite the build system. Configuration
variables should be included using gcc parameter '-include'
*: Replaced bunch of comments with newlines

In some files, /*---*/ strings were used to delimit 80 characters. I can't read
this...
protothreads: Fix unused warning in PT_BEGIN macro

The PT_BEGIN declares the PT_YIELD_FLAG variable, but it does not
have to be necessarilly used. This causes unused variable
warning. Fixed by adding adding "unused" GCC attribute to the variable.
uip: Ignore strict-aliasing warnings caused by the BUF macro

Added #pragma GCC diagnostic ignored "-Wstrict-aliasing" to force gcc to ignore
strict aliasing warnings occuring in various files.
uip: Fix unused label warning

The ip_send_nolen: label is not used unless UIP_UDP is enabled. Fixed by
adding #ifdef.
protosocket: Removed unused parameter on buf_bufdata

Removed unused parameter "len" in the buf_bufdata function.
protosocket: Add explicit typecast to psock_send_P

Assigment of PGM_P to sendptr field of the psock struct was causing build
warnings. Added explicit cast to prevent this.