issue 8723: Changed doc for cv::imwrite to reflect correct default flag used for png compression strategy.

autorotate in-memory jpegs (#8492)

* autorotate in-memory jpegs

* correct indentation (4 spaces)

* imgcodecs: don't apply EXIF rotation for unloaded images

* videoio: don't try to rotate MJPEG stream

* imgcodecs: ByteStreamBuffer::seekoff support all seek "dir"

* imgcodecs: fix condition: "off == egptr() - eback()" is valid offset

 Issue-7310: Updated imwrite doc to correct default setting for IMWRITE_PNG_COMPRESSION and clarified existing doc a bit.

 ExifReader::getExif may enter infinite loop with jpeg image which have no EOI.
For example, bytesToSkip may be set to 0 and fseek seems like fseek(f, -2 , SEEK_CUR) for image that end with RST7(FF D7) instead of EOI.

In cases where the signaure string contains a terminating character,
the std::string member function size returns a smaller value than the
allocated string. In these cases, if you then try to use substr,
you will get an out_of_range exception. This patch remedies the problem.

This patch implements the PAM image format as defined at:
http://netpbm.sourceforge.net/doc/pam.html

The PAM format provides a generic means for storing 2 dimensional information.
This is useful for opencv since there are cases where data gets translated into
non standardized formats, which makes it difficult to store and load this information.

Returning to Win2k value is possible via this CMake option:

    cmake -DOPENCV_EXTRA_FLAGS="/D_WIN32_WINNT=0x0500" ...

UIImages with alpha were ending up with garbage pixels in background (random memory values).  Need to initialize matrix pixels before drawing UIImage with alpha on it.

Note: didn’t fix Grayscale image with alpha stripping alpha in UIImage -> Mat conversion.

The TiffDecoder keeps an open file handle.
As a consequence the file cannot be removed
before the TiffDecoder closes the file.

- fixed width and height order
- removed unused methods
- simplified signature matching
- rewrote pixel format matching in more compact form
- added dimensions number check (only 2 is allowed)
- added target buffer size check
- added debug messages in all failing points

- renamed source files
- guard the contents - always include

Root cause: when calling imread to read the pgm file, when returning with success reading file, the destructor will free the resource which used by memcpy, but in the code, the resource calculation was not correct, therefore, it will cause memory corruption during resource free.