busybox: 'make distclean' first

To ensure we have a clean directory prior to building.
Consistently capitalize BusyBox name

It was written sometimes with the second 'B' lowercase which is
incorrect.
Remove mention of uClibc, replace with "C library"

In prep for removal ov uClibc and insertion of EGLIBC.
Rename uclibc.xml to eglibc.xml, use common

All archs use common eglibc.xml now in cross-tools.
No changes to contents performed, yet, so the book is currently invalid
due to the eglibc section talking about eglibc, but that's OK right now.
Delete cross-tools/{arm,mips}/linux-headers.xml

Were not used, arm and mips both were previously switched to using
common.
Set CLFS_ARCH to just "mips" for MIPS

Setting it with the sed regex could produce a CLFS_ARCH value of
"mipsel" which when used to deal with the Linux kernel would result in
errors since "mipsel" isn't a valid arch for Linux.  "mips" is so let's
just use that.
Convert all uClibc to EGLIBC

Still uses uClibc download, version number, etc.
EGLIBC configure is not present and needs to be.
packages: Enter proper EGLIBC 2.17 info

Using main-book version and download link.
packages: Move EGLIBC into alpha order

Was at the end due to uClibc name before.
eglibc: Steal much of the main book's eglibc

Not yet tested!
Delete uClibc configs patch

No longer needed, we've switched to EGLIBC.
packages: Use svn revision for EGLIBC

Separate out the svn revision from the version number such that we match
the main book's way of doing version numbers and the compressed file.
Install linux headers to cross-tools/include

They aren't needed on the final system so just install them into
${CLFS}/cross-tools/include.  EGLIBC will look for them there.