Make one-bit bit fields unsigned.

VC++ 2015 gives the following warning when compiling jsoncpp:

  json_value.cpp(480): warning C4463: overflow; assigning 1 to bit-field
  that can only hold values from -1 to 0

This warning is correct. A signed one-bit value can only hold 0 and -1.
This is true on gcc and clang, but only VC++ 2015 warns about it.

The code works because the stored value is never compared against 1 or
printed, but the current code is likely to cause surprises or bugs in the
future and should be fixed.

Review URL:

Cr-Original-Commit-Position: refs/heads/master@{#325330}
Cr-Mirrored-Commit: 707c3acd012287f3b4897bedaf57c60fbd4044bd
3 files changed