configure: add a verbose mode

Required for Fedora infrastructure so that the commands used to build
ninja are logged.
Merge pull request #882 from mathstuf/verbose-configure

configure: add a verbose mode
Remove 'Recompacting...' messages.

Recompacting the build log used to be slow, so it made sense to print this
message.  We then made recompaction much faster, but didn't remove this
message back then.

The deps log only has it because the build log had it.

Since both steps are effectively instant in practice, remove these log messages.
zsh-completion: remove use of 'head' with negative offset

Some systems - like OSX - don't come with a version of head that
supports a negative value for the -n flag. Such systems get a message
such as this when tab-completing ninja's -d flag:

    ninja -dhead: illegal line count -- -1

Using sed instead should be more universally supported.
Merge pull request #885 from frasercrmck/zsh_comp_modes

zsh-completion: remove use of 'head' with negative offset
Merge pull request #884 from nico/sshh

Remove 'Recompacting...' messages.