Add warning class (YASM_WARN_UNINIT_CONTENTS) to turn off the

Add warning class (YASM_WARN_UNINIT_CONTENTS) to turn off the
"uninitialized data in code/data section: zeroing" warning.  This can now
be turned off using -Wno-uninit-contents on the command line.

* errwarn.h (yasm_warn_class): Add warning class.
* errwarn.c (yasm_errwarn_initialize): Default it to enabled.

* yasm.c (opt_warning_handler): Add as option.

* xdf-objfmt.c, elf-objfmt.c, bin-objfmt.c, coff-objfmt.c: Change warning
class for this warning.

svn path=/trunk/yasm/; revision=1307