Fix getQuote.yahoo for multiple timezones

[pverspeelt]

When getQuote.yahoo was called it genereted errors when quotes from multiple timezones were involved. Fixed so everything is forced to the local timezone.

Following code now works correctly:

library(quantmod)
metrics <- yahooQF(c("Name", "Volume", "P/E Ratio", "Dividend Yield", "Shares Outstanding"))
symbols <- c("MSFT", "GOOG", "FAGR.BR")
stats <- getQuote(symbols, what = metrics)

Fixes #246