#77 Made variable location more efficient and modular.

[Jim Monte]

Variables curplot, curplotname, curplottitle, and curplotdate are frequently required. This patch finds them more efficiently. Vectors being treated as variables are separated into their own function. Also the search for a variable name was documented more completely.

[Jim Monte]

See patch #78 for a minor modification

[Jim Monte]

Code for this patch as well as the minor addition in patch #78 is available in branch beta_jdm

commit 5260904aa4eb27ffa6c0c81a32534e3712445d73
Date:   Mon, 9 Dec 2019 16:18:31 -0500

    Made cp_enqvar() mode modular by adding a separate function to handle the case of a vector. Lists are more efficiently handled by moving common comparisons out of the loop over elements. The first argument of cp_enqvar() is changed from char * to const char * since the name of the variable being found is not altered by the function.