The 'details' URL sometimes didn't work because
of a failure to properly encode the data tag part.
In particular, square brackets were not handled
correctly by most browsers (konqueror being the only
known exception).

The most important change of this patch
is a restructring of the database schema
in order to better support current
and future use cases.

In particular, the 'result' table has been reduced
in size (which is important since this table is
the one that will grow on a regular basis), and
a 'bmcontext' table has been introduced as an extra
structural level that is expected to make certain
queries faster than they would have otherwise been
(due to reduced need for complex join expressions
etc.).

Time ranges are now specified using either
Unix timestamps or 'first' or 'last'. The
option of specifying a SHA-1 value was
considered not to be particularly useful
in practice. This option has therefore
been obsoleted to simplify the code.

This patch adds support for negative result values
to BM (thus allowing all real values).

A typical use case for negative values is a benchmark
that measures the difference between two implementations
of the same problem/task.

In order to support negative values, the formula for
computing the relative difference between v1 and v2
has been changed from

    (a - b) / (b + 1)
(or (a - b) / (a + 1) )

to

    (a == b) ? 0 : ((a - b) / max(|a|, |b|))

Note that adding 1 in the first formula was necessarry to
allow for zero values. This is no longer needed.

Note also that the new formula doesn't allow direct
selection of the normalization base (i.e. the denominator),
but rather automatically choosing the one with the largest
magnitude. This is assumed not to be a problem, and also
has the interesting property that the absolute value of
the expression is bounded by 2.

This patch also renames the term "current change" to "last difference".

The 'get rankedbenchmarks' request now considers only
benchmarks matching a certain filter. E.g. specifying
'Graphics*' as the test case filter and '*' for the
test function and data tag filters, ensures that only
benchmarks with test cases beginning with "Graphics"
will be processed.

The context part of the configuration of
a benchmark summary page may be interactively
manipulated using HTML <select> menus for
the individual components (metric, platform,
host, and branch). This patch both speeds up
the interactive selection and fixes a bug
that caused the selection from going haywire
(due to improper handling of asynchronous
communication).

This patch also involves a small visibility
change: Rather than just hiding the
non-matching options in each menu, all
available values are now shown, but only
the matching ones are selectable
(i.e. enabled.). WARNING: Manipulating
the disabled attribute of an <option>
element doesn't seem to be supported by
all web browsers.

The number of rows of the benchmark summary
table is now shown in the top-left cell.

The most important change of this commit is that the
'iterations' component of the result value is gone.
Now the result value represented by just the
final real-valued result, rather than two integer
components: (accumulated) result and number of
iterations.

NOTE: The old file format is still accepted,
and when an iterations component is present, the result
component will be divided by this one.

The other significant change of this commit is that
indexes are added to the database scheme to speed up
queries. This only affects the 'initdb'
command-line option, though.