xterm fails ungracefully when saveLines resource value is too large

[Ted Unangst]

Synopsis: xterm fails ungracefully when saveLines resource value is too large
Category: system

System : OpenBSD 6.1
Details : OpenBSD 6.1 (GENERIC.MP) #6: Mon May 22 20:34:30 CEST 2017
Architecture: OpenBSD.amd64
Machine : amd64
xterm: Error 91, errno 12: Cannot allocate memory
Reason: Alloc: calloc() failed on rows
This error message is completely unhelpful from a user standpoint. I didn't know if this was system resource starvation or something else. A better way to handle this situation would be to set saveLines within xterm to the maximum and print a warning that the saveLines variable is too large.

xterm is mainted outside openbsd. we're not likely to maintain a custom patch
for this.