Remove unused variables. Instead of overriding non-standard variables
such as ARCH and PROF, use standard variables CFLAGS and LDFLAGS to
override Makefile settings. Move dependencies generated by `make dep` to
a separate file.

needed when installing a new Redis version. Thanks to Scott Kevill.
Fixes issue #335.

To do so, the Makefile stores the contents of the MALLOC environment
variable in a file named .make-malloc. When the contents of this file
and the MALLOC variable are not equal, it forces a rebuild of the Redis
source tree.

A side-effect of this change is that choosing an allocator can now be
done using the single MALLOC variable instead of USE_TCMALLOC,
USE_JEMALLOC and so forth. These variables continue to work for
backwards compatibility.

This change moves the build instructions for dependencies to a separate
Makefile in deps/. The ARCH environment variable is stored in a
.make-arch file in the same directory as the Makefile. The contents of
this file is read and compared to the current ARCH, and, on a mismatch
triggers rebuilding the entire source tree.

When file .make-arch exists and matches with ARCH from the environment,
the dependencies are assumed to already be built.

The new "clean" target only cleans the Redis source tree, not its
dependencies. To clear the dependencies as well, the "distclean" target
can be used.

Revert "Use the new install script as make install target. Message about install script requiring root changed a bit to make it more evident."
After talking with Pieter he changed my mind about this, it is better to
have a simpler install script that works everywhere, and the complex one
can be always executed if needed by hand. We'll make possibly a new
target for the full featured installation script, and even suggest it
after a Make install.

This reverts commit f1e60d75.

Use the new install script as make install target. Message about install script requiring root changed a bit to make it more evident.

Lua math.random and math.randomseed replaced with our own version based on redisSrand48(). Seed initialized to the same value at every EVAL/EVALSHA call.

libc neutral random function derived from a drand48() implementation added. Will be used to replace Lua's math.random implementation.

Added a 'runtest' script that is responsible to check if Tcl is available and run the test. This is invoked from Makefile as well.

top level Makefile now just a proxy. Doing make clean inside src now does a full clean including deps, not just Redis source. Thanks to Pieter for the top level Makefile proxy trick.

echo with escape sequences isn't portable. Use printf instead.