Fix the x87 FP register printout when issuing the “info float” command.

Consider the following simple program:

.globl  _start
.text
_start:
      fldt    val
.data
      val: .byte 0x00,0x00,0x45,0x07,0x11,0x19,0x22,0xe9,0xfe,0xbf

With current GDB on x86-64 GNU/Linux hosts, after the moment the fldt
command has been executed the register st(0) looks like this,
according to the “info regs” output (TOP=7):

  R7: Valid   0xffffffbffffffffeffffffe922191107450000 -0.910676542908976927

which is clearly wrong (just count its length).  The problem is due to
the printf statement (see patch) printing a promoted integer value of
a char argument "raw[i]", and, since char is signed on x86-64
GNU/Linux, the erroneous “ffffff” are printed for the first three
bytes which turn out to be "negative".  The fix is to use gdb_byte
instead which is unsigned (and is the type of value_contents(), the
type to be used for raw target bytes anyway).  After the fix the value
will be printed correctly:

  R7: Valid   0xbffee922191107450000 -0.910676542908976927

gdb/
2013-04-19  Vladimir Kargov <kargov@gmail.com>
	    Pedro Alves  <palves@redhat.com>

	* i387-tdep.c (i387_print_float_info): Use gdb_byte for pointer to
	value contents.

gdb/testsuite/
2013-04-19  Vladimir Kargov  <kargov@gmail.com>
	    Pedro Alves  <palves@redhat.com>

	* gdb.arch/i386-float.S: New file.
	* gdb.arch/i386-float.exp: New file.

gdb/i387-tdep.c

@@ -298,7 +298,7 @@ i387_print_float_info (struct gdbarch *gdbarch, struct ui_file *file,
 
 	  if (value_entirely_available (regval))
 	    {
-	      const char *raw = value_contents (regval);
+	      const gdb_byte *raw = value_contents (regval);
 
 	      fputs_filtered ("0x", file);
 	      for (i = 9; i >= 0; i--)