install-sh: updated to support multiple source files as arguments

Version 7.29.0 uses Makefiles generated with a newer version of the
autotools than the previous 7.28.1. These Makefiles try to install
e.g. header files by calling install-sh with multiple source files as
arguments. The bundled install-sh is to old and does not support this.

The problem only occurs, if install-sh is actually being used, ie. the
platform install executable is to old or not usable. Example: Solaris
10.

The files install-sh and mkinstalldirs are now updated with the automake
1.11.3 versions. A better fix might be to completely remove them from
git and force the files to be added/created during buildconf.

Bug: http://curl.haxx.se/bug/view.cgi?id=1195
Reported by: Rainer Jung