"Correct" license from LGPL2 to LGPL2.1

"Correct" license from LGPL2 to LGPL2.1

Back in commit 7469f26a33c072169d6ed929352eda06562ffe3f when the COPYING
file was added to the repository and the project was "licensed," the
license file was

                     GNU LESSER GENERAL PUBLIC LICENSE
                          Version 2.1, February 1999

However, the license was abbreviated as LGPL2 in various places (pretty
much everywhere, actually), due to my own ignorance/carelessness.  (I was
distinguishing it from shiny new version 3, released 6 months earlier.)

Version 2 of LGPL is the "Library General Public License," published in
June 1991: https://www.gnu.org/licenses/old-licenses/lgpl-2.0.html

Note that this ambiguity persists for most of the project's lifetime.  For
example, the original debian/copyright in 8adc9dac1d61f34ce85e3cbad1478e3e6ffe2b8e
said "LGPL2" bug in 4545f8b929cc562a1231c0ceb067e9d8e58a0de7 (2009, a year
later) it is changed to LGPL2.1 to satisfy Debian's lintian checks.  (It's
remained LGPL2.1 ever since.)

"Correct" the record by changing LGPL2 references to LGPL2.1.

Signed-off-by: Sage Weil <sage@redhat.com>