Add force_length and adjust_length properties.
Add force_length and adjust_length properties.

The reporter on kdenlive bug 2003 reports another user on IRC had the
same problem with clips being too long. Change the default length
adjustment to be more safe and add new properties to affect the
heuristic for other applications that might want a different behavior.
adjust_length applies a plus/minus operand to the detected length.
force_length provides a brute force length override.

j-b-m/mlt,ttill/MLT-roto,ttill/MLT-roto,mltframework/mlt,xzhavilla/mlt,ttill/MLT,mltframework/mlt,gmarco/mlt-orig,ttill/MLT-roto-tracking,wideioltd/mlt,xzhavilla/mlt,anba8005/mlt,wideioltd/mlt,ttill/MLT,zzhhui/mlt,gmarco/mlt-orig,ttill/MLT-roto-tracking,wideioltd/mlt,siddharudh/mlt,siddharudh/mlt,ttill/MLT,ttill/MLT-roto-tracking,mltframework/mlt,zzhhui/mlt,ttill/MLT-roto-tracking,siddharudh/mlt,zzhhui/mlt,zzhhui/mlt,siddharudh/mlt,anba8005/mlt,mltframework/mlt,j-b-m/mlt,xzhavilla/mlt,xzhavilla/mlt,mltframework/mlt,anba8005/mlt,zzhhui/mlt,j-b-m/mlt,anba8005/mlt,ttill/MLT-roto-tracking,siddharudh/mlt,gmarco/mlt-orig,gmarco/mlt-orig,j-b-m/mlt,anba8005/mlt,ttill/MLT-roto,anba8005/mlt,ttill/MLT-roto,ttill/MLT-roto-tracking,xzhavilla/mlt,ttill/MLT,anba8005/mlt,siddharudh/mlt,zzhhui/mlt,ttill/MLT-roto,ttill/MLT-roto,gmarco/mlt-orig,j-b-m/mlt,siddharudh/mlt,ttill/MLT-roto,ttill/MLT-roto-tracking,wideioltd/mlt,ttill/MLT,wideioltd/mlt,wideioltd/mlt,ttill/MLT,anba8005/mlt,xzhavilla/mlt,ttill/MLT,xzhavilla/mlt,xzhavilla/mlt,j-b-m/mlt,gmarco/mlt-orig,ttill/MLT-roto,gmarco/mlt-orig,j-b-m/mlt,mltframework/mlt,ttill/MLT-roto,ttill/MLT,j-b-m/mlt,gmarco/mlt-orig,ttill/MLT-roto-tracking,ttill/MLT,zzhhui/mlt,ttill/MLT-roto-tracking,xzhavilla/mlt,siddharudh/mlt,zzhhui/mlt,j-b-m/mlt,mltframework/mlt,mltframework/mlt,zzhhui/mlt,gmarco/mlt-orig,wideioltd/mlt,siddharudh/mlt,mltframework/mlt,mltframework/mlt,wideioltd/mlt,j-b-m/mlt,anba8005/mlt,wideioltd/mlt