BUG: Fix exceptions being swallowed by fromiter.

All exceptions from underlying iterator were being collapsed into a
generic one. This allows the original exception to propagate.

Closes gh-2592.
TST: Add tests for exceptions raised by fromiter.

This improves the testing of the edge cases.

Work done with @certik.
BUG: Remove xrange that slipped into test_numeric.py.
STY: Fix trailing whitespace and replace test doctrings by comments.
BUG: Allow to pad arrays by zero entries.

np.pad will now accept a pad_width containing zeros. The functionality
was already implemented, but validation of input was too strict.
TST: New test to ensure np.pad allows pad_width of zero.
Merge pull request #3506 from josteinbf/arraypad-padwidth-zero

Allow pad_width of zero in np.pad
Merge pull request #3500 from charris/fix-3592

Fix exceptions being swallowed by fromiter.
BUG: Fix creation of string arrays from object types
STY: Formatting changes
ENH: vectorize boolean comparisons of floats

the new code will more often propagate the invalid floating point
exception if comparing against nan, so allclose now ignores it (but
still returns False)
Merge pull request #3507 from juliantaylor/vectorize-cmp

ENH: vectorize boolean comparisons of floats
Merge pull request #3491 from ContinuumIO/astype_fix2

Fix creation of string arrays from object types
BUG: Check earlier for higher priority in binary operators, add test

Fixes #3375
Add regression tests for pickleable record arrays
Merge pull request #3501 from inducer/master

Fix "numpy scalar * array-like == performance horror"
Merge pull request #3510 from mwtoews/master

Add regression tests for pickleable record arrays