Added conditional breakpoints

[TamaMcGlinn]

Added support for conditional breakpoints for gdb. To test this; I used the following fizzbuzz in C++:

#include<iostream>
using std::cout;
using std::endl;

void print_fizzbuzz(int n) {
  const bool mod5 = n % 5 == 0;
  const bool mod3 = n % 3 == 0;
  if (mod3 && mod5) {
    cout << "FizzBuzz" << endl;
  } else if (mod3) {
    cout << "Fizz" << endl;
  } else if (mod5) {
    cout << "Buzz" << endl;
  } else {
    cout << n << endl;
  }
}

void fizzbuzz() {
  for (int i = 1; i <= 100; ++i) {
    print_fizzbuzz(i);
  }
}

int main() {
  fizzbuzz();
  return 0;
}

Using this branch, I can add a breakpoint for instance on line 6 with <vebugger-leader>k and then type in if n == 5. Everything I tested works:

• Setting the breakpoint before or after the debugger has started
• Toggling the breakpoint with or without a condition works; when removing, the condition passed in is ignored. The highlight correctly updates when you add conditional breakpoints, although you can't see the difference between a conditional breakpoint and a regular one.
• Toggling normal breakpoints still works, because the empty string is passed as the condition, which will just add a space at the end of the command passed to the debugger, which it ignores.

Note: I have not yet tested other debuggers than gdb. Presumably we should add it for others that support it as well.

Adding support for #95 was easier than I thought!

[TamaMcGlinn]

I should note that it is easy to mistakenly add a condition such as 'n == 5' instead, which will never be true. I'm not sure why gdb requires the if, and maybe it should be hidden inside vebugger, actually. That would mean we need to test if there is a non-empty condition, and only add 'if '.l:breakpoint.condition if the string is non-empty.

[TamaMcGlinn]

Although it would still be better to show the condition of a conditional breakpoint as soon as you put the cursor over it, I just realised an easy way to show the condition is to edit it again using <vebugger-leader>k - if we can pre-populate the input window with the current condition, then you can just view it without editing and close it again, effectively recreating the same conditional breakpoint.