Proposal for renaming/replacing SWIG-Mapscript functions

[ghschier]

The global functions in SWIG regarding HTTP-Headers are confusingly named and do not act as expected.
My propsals would be:

msIO_getAndStripStdoutBufferMimeHeaders()
Does in fact remove all headers (including Status), what is good.
Rename therefore to msIO_getAndStripStdoutBufferHeaders()

msIO_stripStdoutBufferContentHeaders()
Remove or mark as deprecated. Use msIO_getAndStripStdoutBufferHeaders() instead

msIO_stripStdoutBufferContentType()
Does obviously not return the content type, if there is more than 1 header set (see #6762)
Remove or mark as deprecated. Use msIO_getAndStripStdoutBufferHeaders() instead (the function returns the headers in a hashTableObj)

Conclusion
There is only 1 function necessary to handle the HTTP-headers.
The function msIO_getAndStripStdoutBufferHeaders() would replace the 3 existing functions.