[Libguestfs] enable -Werror and all of gcc's warning options

[Jim Meyering]

Here is a bunch of small patches to make fish/ build
with most warnings enabled:

  [1/9] edit.c: avoid warning about signed/unsigned comparison
  [2/9] fish.c: avoid warnings
  [3/9] tilde.c: avoid a warning
  [4/9] fish.c: avoid "assignment discards qualifiers..." warning
  [5/9] fish.c: avoid signed/unsigned-comparison warning
  [6/9] fish.c: don't perform arithmetic on void* pointers
  [7/9] destpaths.c: avoid signed/unsigned-comparison warning
  [8/9] generator.ml: avoid signed/unsigned-comparison warning in fish/cmds.c
  [9/9] fish/: enable -Werror and all of gcc's warning options

 b/fish/Makefile.am |    5 ++---
 b/fish/destpaths.c |    3 +--
 b/fish/edit.c      |    6 +++---
 b/fish/fish.c      |    2 +-
 b/fish/fish.h      |    2 +-
 b/fish/rc.c        |    3 ---
 b/fish/tilde.c     |    9 +++------
 b/src/generator.ml |    5 ++---
 fish/fish.c        |    9 ++++-----
 fish/fish.h        |    7 ++++++-
 10 files changed, 23 insertions(+), 28 deletions(-)