Speed up dropping lines
Remove log statement
Initialize screen_char_t’s in PTYTask thread for ascii strings. Combine ALTSEM_FG_DEFAULT and ALTSEM_BG_DEFAULT into one value so totally default characters are 0s and calloc initializes all the fields of screen_char_t except code for ascii data. Add ALTSEM_REVERSED_DEFAULT so foreground and background can take each other’s default values in reverse video.
Improve performance on very long lines by assuming there are no DWC's until one is seen, which allows a faster algorithm for counting the number of lines since we don't care about DWCs that get wrapped to the next line.
reduce number of outstanding execute calls with minimal performance penalty of 4%
Fix bug in Autocomplete that limits size of prefix to 1 byte