Release 1.6.15 (released 1 Jul 2016 -- compared to 1.6.14)

• Improved ImageCache/TextureSystem statistics: for the "top 3" stats, print the top 3 that aren't broken. Also print a count & list of broken/invalid files. #1433
• Change in behavior writing JPEG files when XResolution & YResolution are not provided, but a PixelAspectRatio is requested. Previously, we obeyed the JPEG/JFIF spec exactly, but it turns out that popular apps including PhotoShop and Nuke use the field differently than the spec dictates. So now we conform to how these apps work, rather than to the letter of the spec. #1412
• IC/TS: add ability to retrieve various per-file statistics. #1438
• Windows UTF-8 filename safety fixes. #1420
• ImageOutput: fix cases with native data but non-contiguous strides. #1416
• Make FindOpenEXR.cmake more robust when the version number is embedded in the library name. #1401
• Fix build breaks for gcc 6. #1339 (1.7.2/1.6.11) #1436
• More robust detected of when OpenEXR is tiled (for weird files). #1441
• Various Windows compilation and warning fixes.
• strutil.h: added replace(). #1422
• thread.h: added mutex_pool. #1425