Avoid changing strings when complexifying

[sseraj]

Description

The current pattern matching does not check whether the patterns are used in strings that are printed out. For example in mdolab/adflow#229, I ran into a problem where a sequence of "======" being used as a separator was converted to ".ceq..ceq..ceq.". This does not necessarily break the compilation, but it can if the line exceeds the character limit.

Steps to reproduce issue

1. Build the complex version of ADflow.
2. Check src_cs/BCData.F90 for .ceq..ceq..ceq.

Current behavior

Some strings are substituted with complexified functions.

Expected behavior

Strings should stay the same.