[benchtests] Use inputs file for modf

The modf benchmark can now use the framework since the introduction of
output arguments.
Make bench.out in json format

This patch changes the output format of the main benchmark output file
(bench.out) to an extensible format.  I chose JSON over XML because in
addition to being extensible, it is also not too verbose.
Additionally it has good support in python.

The significant change I have made in terms of functionality is to put
timing information as an attribute in JSON instead of a string and to
do that, there is a separate program that prints out a JSON snippet
mentioning the type of timing (hp_timing or clock_gettime).  The mean
timing has now changed from iterations per unit to actual timing per
iteration.
Detailed benchmark outputs for functions

This patch adds an option to get detailed benchmark output for
functions.  Invoking the benchmark with 'make DETAILED=1 bench' causes
each benchmark program to store a mean execution time for each input
it works on.  This is useful to give a more comprehensive picture of
performance of functions compared to just the single mean figure.
Fix scalb spurious "invalid" exceptions (bug 16770).

This patch fixes bug 16770, spurious "invalid" exceptions from scalb
when testing whether the second argument is an integer, by inserting
appropriate range checks to determine whether a cast to int is safe.
(Note that invalid_fn is a function that handles both nonintegers and
large integers, distinguishing them reliably using functions such as
__rint; note also that there are no issues with scalb needing to avoid
spurious "inexact" exceptions - it's an old-POSIX XSI function, not a
standard C function bound to an IEEE 754 operation - although the
return value is still fully determined.)

Tested x86_64 and x86.

	[BZ #16770]
	* math/e_scalb.c (__ieee754_scalb): Check second argument is not
	too large before casting to int.
	* math/e_scalbf.c (__ieee754_scalbf): Likewise.
	* math/e_scalbl.c (__ieee754_scalbl): Likewise.
	* math/libm-test.inc (scalb_test_data): Add more tests.