Do not call MacroExpander::popMacro() from MacroExpander::~MacroExpander().

Do not call MacroExpander::popMacro() from MacroExpander::~MacroExpander().
MacroExpander::popMacro() assumes that the macro being popped has been fully parsed.
This may not be true for MacroExpander destructor which may get called anytime the compiler decides to abort the compilation process.
This patch just deletes the macro-contexts pushed in the stack without validating the parse state of current macro.

BUG=348
Committed: https://code.google.com/p/angleproject/source/detail?r=1227

[kbr1, 2012-07-18 00:08:28]

This needs a regression test.

[Alok Priyadarshi, 2012-07-18 01:46:15]

On 2012/07/18 00:08:28, kbr1 wrote:
> This needs a regression test.

I cannot think of a way to test this condition. This patch only avoids a
harmless assert in debug build. In fact the bug description is not accurate. The
conformance tests do pass if you ignore the assert.

[kbr1, 2012-07-18 01:56:55]

Unfortunate, but OK -- LGTM.