: Minor fixes

Hi,

Some random things I've fixed while reading the code, they're
unrelated changes, but I think it's better to send in one shot.

Diff stat:

 Documentation/core-tutorial.txt |    9 ++++-----
 builtin-commit-tree.c           |    3 +--
 cache.h                         |    2 +-
 entry.c                         |   14 +++++++-------
 read-cache.c                    |   16 ++++++++--------
 5 files changed, 21 insertions(+), 23 deletions(-)

Luiz Fernando N. Capitulino