How about make install of manpage configurable

[sandy-lcq]

I am doing cross compile of squashfs-tools, and met one issue: if the build host has help2man, then install-manpages.sh will run mksquashfs-manpage.sh, then run mksquashfs -help, but the built out mksquashfs is for running on target. not for running on build host, even maybe have different arch with build host, which will cause error.

How about make the install of manpage configurable? So user can select to not use help2man.