Fix compiling for SPARC_SE:

Fix compiling for SPARC_SE:
- change include from exec_context.hh -> threadcontext.hh
- g++ 4.0.3 complaint about broken code (which it was).
- bad merge thread_context -> exec_context

src/arch/sparc/isa/includes.isa:
    Fix SPARC_SE for exec_context->thread_context switch
src/arch/sparc/regfile.hh:
    fix g++ 4.0.3 complaint about broken code (which it was).
src/cpu/thread_context.hh:
    fix bad merge

--HG--
extra : convert_revision : f5bab822d5c25177756e9890e143b0ad8d704201