Provides full coverage for shared functions (shared.js)

[erikyo]

Covers 'shared' functions with tests

@johnhooks can you take a look at this? I tested the result with the original function, and with the current updated code and it seems there are some issues, and this condition cannot be verified:

gettext-parser/lib/shared.js

Lines 116 to 120 in d8dcbee

	// ensure that the line never ends with a partial escaping
	// make longer lines if needed
	while (curLine.substr(-1) === '\\' && pos + curLine.length < len) {
	curLine += str.charAt(pos + curLine.length);
	}

Precisely in this row (from the original shared.js before any modification):
while (curLine.substr(-1) === '\\' && pos + curLine.length < len) {

It was intended \\\\ and not \\?